JP3856501B2 - Optical device, optical correction method, and projection display device - Google Patents

Description

ただし、ｍ_Ｓは前記第２のレンズ手段のサジタル近軸像点での虚像倍率、ｎ_１は前記第１の平面板部材の屈折率、ｎ_１′は前記第１の平面板部材の媒質の屈折率、θ_１は前記第１の平面板部材の媒質から前記平面板部材に入射する、前記第１及び第２のレンズ手段の光軸上光線の入射角、ｎ_２は前記第２の平面板部材の屈折率、ｎ_２′は前記第２の平面板部材の媒質の屈折率、θ_２は前記第２の平面板部材の媒質から前記第２の平面板部材に入射する、前記第１及び第２のレンズ手段の光軸上光線の入射角である。
【００１４】
また、第５の本発明は、光学像を形成する画像形成手段と、前記画像形成手段の光軸上前方に配置された第１のレンズ手段と、前記画像形成手段と前記第１のレンズ手段との間に配置され、正パワーを有する第２のレンズ手段と、前記第１のレンズ手段と前記第２のレンズ手段との間に配置され、色合成手段を構成し、前記光学像を透過する第１の平面板部材と、前記第２のレンズ手段と前記画像形成手段との間に配置され、偏光分離性能を有し、前記光学像を透過する第２の平面板部材とを備え、前記第１のレンズ手段と前記第２のレンズ手段とが、前記画像形成手段上の前記光学像をスクリーン上に拡大投写するように組み合わされており、第２の平面板部材は、片面に偏光選択特性を有する薄膜が設けられ、偏光分離性能を有する所定厚みの透明基板であって、前記第１及び第２の平面板部材は、前記第１及び前記第２のレンズ手段のなす光軸に対して斜めに配置されている光学装置の光学補正方法であって、
前記第１の平面板部材の平面に対する法線と前記第１及び第２のレンズ手段の光軸とを含む平面と、前記第２の平面板部材の平面に対する法線と前記第１及び第２のレンズ手段の光軸とを含む平面とを互いに直交させ、前記第１の平面板部材と前記第２の平面板部材とにより生じる非点収差が、互いに補正するように、前記第１の平面板部材の板厚ｔ_１と前記第２の平面板部材の板厚ｔ_２との関係を、以下の式を満足するように調整することを特徴とする光学補正方法である。
【数４】

ただし、ｍ_Ｓは前記第２のレンズ手段のサジタル近軸像点での虚像倍率、ｎ_１は前記第１の平面板部材の屈折率、ｎ_１′は前記第１の平面板部材の媒質の屈折率、θ_１は前記第１の平面板部材の媒質から前記平面板部材に入射する、前記第１及び第２のレンズ手段の光軸上光線の入射角、ｎ_２は前記第２の平面板部材の屈折率、ｎ_２′は前記第２の平面板部材の媒質の屈折率、θ_２は前記第２の平面板部材の媒質から前記第２の平面板部材に入射する、前記第１及び第２のレンズ手段の光軸上光線の入射角である。
【００１５】
また、第７の本発明は、３原色の色成分を含む光を放射する光源と、
前記光源の放射光を３つの原色光に分解する色分解手段と、
前記色分解手段の３つの出力光のそれぞれが個別的に入射する３つの前置偏光子と、
複屈折性の変化として光学像を形成する複数の画像形成手段と、
前記画像形成手段毎に設けられた、偏波面が互いに直交する偏光成分を分離する偏光分離手段と、
それら各偏光分離手段毎に設けられた、その偏光分離手段からの光を透過させる、正パワーを有する第２レンズと、
前記各偏光分離手段からの光を１つに合成する色合成手段と、
前記色合成手段からの出射光を入射して出射する第１レンズとを備え、
前記各偏光分離手段は、前記第１レンズの光軸に対して斜めに配置された平行平面の、前記光学像を透過する透明基板を有し、その透明基板上には偏光選択性を有する誘電体多層膜が形成されており、
前記色合成手段は、前記３つの原色光のうち２つの光については、前記第１レンズの光軸に対して斜めに配置された平行平面の、透明基板上に波長選択性を有する誘電体多層膜を形成した、前記２つの光をそれぞれ透過するダイクロイックミラーを含んで構成されたものであり、前記３つの原色光のうち残りの１つの光については、前記第１レンズの光軸に対して斜めに配置された平行平面の透明基板の両面に反射防止処理を施した、前記残りの１つの光を透過する光学補正板を含んで構成されたものであり、
前記各第１のレンズと前記各第２のレンズとは、前記画像形成手段上の前記光学像をスクリーン上に拡大投写するように組み合わされており、
前記３つの原色光のうち前記２つの光についての前記色合成手段の前記各ダイクロイックミラーの誘電体多層膜形成面の法線又は前記３つの原色光のうち前記残りの１つの光についての前記色合成手段の前記光学補正板の反射防止面の法線と前記第１レンズ及び第２レンズの光軸とを含む平面と、前記各偏光分離手段の誘電体多層膜形成面の法線と前記第１レンズ及び第２レンズの光軸とを含む平面とが互いに直交しており、
前記３つの原色光のうち前記２つの光についての前記色合成手段の前記ダイクロイックミラーの板厚であって、前記３つの原色光のうち前記残りの１つの光についての前記色合成手段の前記光学補正板の板厚である板厚ｔ_１と、前記３つの原色光に対応する前記偏光分離手段の前記透明基板の板厚ｔ_２とは、以下の条件を満足することを特徴とする投写型表示装置である。
【数４】

ただし、ｍ_Ｓは前記第２レンズのサジタル近軸像点での虚像倍率、ｎ_１は前記ダイクロイックミラー基板又は前記光学補正板の屈折率、ｎ_１′は前記ダイクロイックミラー又は前記光学補正板の媒質の屈折率、θ_１は前記媒質から前記ダイクロイックミラー又は前記光学補正板に入射する、前記第１レンズ又は前記第２レンズの光軸上光線の入射角、ｎ_２は前記偏光分離手段の透明基板の屈折率、ｎ２′は前記偏光分離手段の媒質の屈折率、θ_２は前記媒質から前記偏光分離手段の偏光分離面に入射する、前記第１レンズ又は前記第２レンズの光軸上光線の入射角である。
【００２４】
以上の様な構成により、例えば色合成光学系で発生する非点収差を良好に補正することができ、しかも投写光学系をコンパクトに構成できる。従って、本発明の光学装置を用いた投写型表示装置では、例えば色合成光学系を有する１つの投写レンズで構成した場合でも、非常に高い解像度の投写画像を表示できる。
【００２５】
【発明の実施の形態】
本発明の実施の形態について、添付図面を参照しながら説明する。
【００２６】
色合成手段としてのダイクロイックミラーによる非点収差は、図１に示すように、光軸に対して斜めに傾いた平行平面の透明板Ｐを、収束光が透過する場合、透明板Ｐと媒質（この場合は空気）との境界面の法線と、収束光の主光線Ｏとを含む平面を入射面とし、その入射面に垂直な平面内にある光線をサジタル光線Ｓ、その入射面に平行な平面内にある光線をメリディオナル光線Ｍとすると、透明板Ｐを通過したサジタル光線Ｓとメリディオナル光線Ｍが、それぞれ主光線Ｏと交わる点がＱ_S、Ｑ_Mとなって異なることによって発生する。又、この場合の点Ｑ_Sと点Ｑ_Mとの間隔は非点隔差と呼ばれる。
【００２７】
図２（ａ）に示すように、互いに入射面が直交する２つの平行平面の透明板Ｐ１、Ｐ２を配置すれば、透明板Ｐ１、Ｐ２でそれぞれで定義されるサジタル光線とメリディオナル光線は互いに入れ替り、非点収差も互いに打ち消し合うように作用する。透明板Ｐ１と透明板Ｐ２の間にパワーを有するレンズ系が無い場合、光軸に対する傾き角、板厚、および透明板の屈折率を同じにすれば非点収差を補正することができる。
【００２８】
ただし、色合成手段としてのダイクロイックミラーの他に非点収差を補正するための透明板を、投写手段である投写レンズと画像形成手段であるライトバルブとの間に追加する場合、投写レンズは非常に長いバックフォーカスを有するものが要求される。
【００２９】
そこで、図２（ｂ）の示すように、投写レンズを長い空気間隔を有する第１レンズ群Ｌ１と第２レンズ群Ｌ２で構成し、第１レンズ群Ｌ１と第２レンズ群Ｌ２との間に色合成光学系を配置し、さらに第２レンズ群Ｌ２とライトバルブＬＶとの間に色合成光学系のダイクロイックミラーとなる平行平面の透明板Ｐ１で発生する非点収差を補正するような平行平面の透明板Ｐ２を配置すれば、実質的に長いバックフォーカス（第１レンズ群Ｌ１からライトバルブＬＶまでの間隔）を実現しながらレンズ外径の小さい投写レンズが実現できる。
【００３０】
この場合、色合成光学系と、色合成光学系の透明板Ｐ１で発生する非点収差を補正する透明板Ｐ２との間に、パワーを有する第２レンズ群Ｌ２が配置されるため、色合成光学系で発生する非点隔差ｄ₁′は次の式で表される。
【００３１】
【数６】

【００３２】
ただし、ｍは第２レンズ群Ｌ２の虚像倍率、ｄ₁は第２レンズ群Ｌ２が無い場合の色合成光学系で発生する非点隔差である。
【００３３】
従って、第２レンズ群Ｌ２とライトバルブＬＶとの間に配置される透明板Ｐ２で発生する非点隔差をｄ₂とすると、透明板Ｐ１と、非点収差を補正する透明板Ｐ２との関係は以下の条件を満足するように互いの板厚を設定すればよい。
【００３４】
【数７】

【００３５】
さらに、本発明の光学装置は、偏光子、および検光子の機能を有する偏光分離手段として、偏光ビームスプリッタを用いており、第２レンズ群と結像面との間に偏光ビームスプリッタを配置し、偏光分離面を形成する平行平面の透明板を色合成光学系で発生する非点収差を補正するように配置する。こうすることによって、偏光ビームスプリッタは偏光分離機能と非点収差補正機能とを同時に有することができる。
【００３６】
尚、（数６）からわかるように色合成光学系の透明板Ｐ１（ダイクロイックミラー）で発生する非点隔差ｄ₁′は、第２レンズ群Ｌ２が無い場合の非点隔差ｄ₁と比べて、正パワーを有する第２レンズ群による虚像倍率ｍの２乗分だけ小さくすることができる。この点についても具体的な実施の形態を後述する。
【００３７】
以下に、本発明の光学装置を用いた投写型表示装置の具体的な実施の形態について、図３に示す構成図を用いて説明する。
【００３８】
第２レンズ群６４，６５，６６は、それぞれ対応する偏光ビームスプリッタ５２，５３，５４と接合されている。また、第１レンズ群７１と第２レンズ群６４，６５，６６とで投写レンズを構成し、偏光ビームスプリッタ５２，５３，５４から第１レンズ群７１までの光学系を、反射型ライトバルブ５５，５６，５７上の光学像をスクリーン上に投写する投写光学系と呼ぶことにする。
【００３９】
光源４１の放射光は３原色の色成分を含む光を放射する。コールドミラー４２は可視光を反射し、赤外光を透過するものである。光源４１からの放射光は、コールドミラー４２によって可視光のみが反射され、３枚のダイクロイックミラー４３，４４，４５で構成される色分解光学系により順次緑、青、赤の３原色光に分解される。各原色光は、それぞれ前置偏光子４６，４７，４８に入射し、いずれも略直線偏光となって出射する。略直線偏光となった各原色光は、読み出し光としてミラー４９，５０，５１を経て偏光ビームスプリッタ５２，５３，５４に入射し、反射型ライトバルブ５５，５６，５７側に反射される。反射型ライトバルブ５５，５６，５７は、図１２に示したものと同じような基本構成のものを用いている。
【００４０】
一方、ＣＲＴ５８，５９，６０上に形成された画像は、書き込み光として書き込みレンズ６１，６２，６３によって対応する反射型ライトバルブ５５，５６，５７の光導電層上に結像される。光変調層である液晶層は、光導電層上に形成された画像に応じて、入射する直線偏光の読み出し光を楕円偏光に変調する。変調された読み出し光は反射型ライトバルブ５５，５６，５７の光反射層によって反射されて再び偏光ビームスプリッタ５２，５３，５４に入射し、反射される偏光成分は光源４１側に進行し、透過する偏光成分は第２レンズ群６５，６６，６７に入射する。
【００４１】
第２レンズ群６５，６６，６７からの出射光は、透明板６７、ダイクロイックミラー６８，６９、および平面ミラー７０を組み合わせた色合成光学系により１つの光に合成され、合成された光は第１レンズ群７１に入射する。３つの反射型ライトバルブ５５，５６，５７上の光学像は第１レンズ群７１と第２レンズ群６４，６５，６６により離れた位置にあるスクリーン上に拡大投写される。
【００４２】
尚、透明板６７は、３原色光のそれぞれの色合成光学系で発生する非点隔差を同一にするために挿入されたものである。これにより、３つの偏光ビームスプリッタ５２、５３、５４の各透明板の板厚等を同じにすることが出来ると言う効果がある。
【００４３】
偏光ビームスプリッタ５２，５３，５４、第２レンズ群６４，６５，６６、透明板６７、ダイクロイックミラー６８，６９、ミラー７０、第１レンズ群７１をすべて１つの鏡筒に収納するとよい。こうすると、偏光ビームスプリッタ５２，５３，５４から第１レンズ群７１までの投写光学系を精度良く組み立てることができる。
【００４４】
次に、偏光ビームスプリッタの詳細な構成を図４を参照して説明する。偏光ビームスプリッタ５２，５３，５４、第２レンズ群６４，６５，６６は図３に示した、偏光ビームスプリッタ５２，５３，５４、第２レンズ群６４，６５，６６とそれぞれ同じものである。
【００４５】
枠体８１、透明板８２，８３、偏光分離ミラー８４で構成される容器の空間には液体８５が充填されている。偏光分離ミラー８４は誘電体多層膜を透明なガラス基板上に蒸着したものであり、偏光分離面となる誘電体多層膜面は周囲の液体８５と密着することで偏光分離性能を示す。
【００４６】
偏光ビームスプリッタ５２，５３，５４に用いる液体８５は、透明であること、光学特性が均一であること、凝固点が低いこと、沸点が高いこと、安価であることなどが要求される。上記条件をほぼ満足する液体として、本実施の形態ではエチレングリコール５５重量％、ジエチレングリコール３０重量％、グリセリン１５重量％の３種混合液を用いている。この３種混合液は光学性能が良好であり、しかも凝固点が−５２℃、沸点が＋１９８℃と、本実施の形態の投写型表示装置の使用環境では問題なく使用できる。また、コストも安価であり、ガラスプリズムを用いた場合に比べて、重量、コストともに圧倒的に有利である。
【００４７】
液体としては他にエチレングリコールを主成分として上記３種類液体の混合比を変えたものや、純エチレングリコール、またはエチレングリコール水溶液などを用いてもよい。但し、水溶液は枠体９１の材質がアルミニウムの場合、アルミニウムと水の反応により酸化アルミニウムが析出し、液体が次第に白濁する場合があるので注意を要する。また、液体として、組立時には液体であるが組み立て完了後は固体またはゲル状となる材料（例えば信越化学工業（株）ゲル状透明シリコーン樹脂ＫＥ１０５１）などを用いてもよい。
【００４８】
偏光選択性ミラー８４は、ガラス基板上に低屈折率膜層と高屈折率膜層とが交互に積層された誘電体多層膜を蒸着したもので、Ｐ偏光の透過率が最大となるブリュースタ角と誘電体多層膜の干渉効果を利用したタイプを採用している。このタイプの偏光分離ミラーは、外部媒質の屈折率をｎ_M、低屈折率層の屈折率をｎ_L、高屈折率層の屈折率をｎ_Hとすると光線の最適入射角θ_Mは次式で求められる。
【００４９】
【数８】

【００５０】
（数８）の条件を満たしていれば、Ｐ偏光の透過率を１００％に保ちながらＳ偏光は誘電体多層膜の層数を増やすことで反射率を高くすることがでる。
【００５１】
本実施の形態の偏光分離ミラー８４は低屈折率膜としてフッ化マグネシウム（屈折率１．３９）、高屈折率膜として二酸化チタン（屈折率２．３０）を用い、液体８６，８７，８８の屈折率は１．４４であるので（数８）より、最適な光線入射角は５５．６°となる。従って、偏光選択性ミラー８４は投写光学系の光軸となす角度が３４．４°となるように傾けて配置されている。誘電体多層膜は１３層構成であり、Ｓ偏光の反射率ピークが入射する３原色光のそれぞれの中心波長となるように誘電体多層膜の各膜厚を設定している。
【００５２】
この様に、反射率については、誘電体多層膜の層数が関係しており、反射波長の中心波長については、誘電体多層膜の各膜厚が関係している。
【００５３】
また、反射波長帯域を広帯域化する構成としては、次の２つの構成がある。
【００５４】
即ち、第１の構成としては、偏光分離ミラー８４は、ガラス基板の両面にＳ偏光成分の反射波長帯域が異なる第１の誘電体多層膜と第２の誘電体多層膜をそれぞれ形成して構成すれば、全体としてＳ偏光の反射波長帯域をより広帯域化できる。こうすることにより、偏光ビームスプリッタ５２，５３，５４に入射する光の波長帯域が広帯域の場合でも良好な偏光分離性能を示すことができる。
【００５５】
又、第２の構成としては、偏光分離ミラー８４は誘電体多層膜を構成する低屈折率層と高屈折率層の屈折率差が大きいほどＳ偏光を反射する波長帯域を広くすることができる。本実施の形態の偏光分離ミラー８４では、できるだけＳ偏光成分の反射波長帯域を広げるために、透明で耐久性に優れた材料として使用できる最も低い屈折率材料であるフッ化マグネシウムと、最も高い屈折率材料である二酸化チタンを用いたが他の屈折率の薄膜材料を用いてもよい。例えば、低屈折率層として二酸化珪素（屈折率１．４６）、三酸化二アルミニウム（屈折率１．６２）など、また、高屈折率層として硫化亜鉛（屈折率２．３０）、二酸化セリウム（屈折率２．３０）、二酸化ジルコニウム（屈折率２．０５）、五酸化二タンタル（屈折率２．１０）、二酸化ハフニウム（屈折率２．００）などを用いることができる。但し、その場合も、偏光分離ミラー８４の配置角度は（数８）の条件を満足するように設定する必要がある。
【００５６】
図４に示すように、透明板８２へ垂直に入射するＳ偏光８６は液体８５を透過して偏光分離ミラー８４へ５５．６°の角度で入射する。偏光分離ミラー８４により反射されたＳ偏光８７は液体８５を通過し、透明板８３から反射型ライトバルブ側に出射する。反射型ライトバルブにより反射された光は再び透明板８３、液体８５を透過して偏光分離ミラー８４に入射する。反射型ライトバルブにより変調されたＰ偏光８８は偏光分離ミラー８４、液体８５、第２レンズ群８８を順次透過して、図３に示した第１レンズ群７１側に進み、変調されないＳ偏光は再び偏光分離ミラー８４によって透明基板８２側に反射される。
【００５７】
図３に示した構成では、図２（ｂ）に示した図のように色合成光学系を構成する透明板６７の反射防止面、及びダイクロイックミラー６８，６９の色合成面の法線と投写光学系の光軸とを含む平面と、偏光ビームスプリッタ５２，５３，５４の偏光分離面の法線と投写光学系の光軸とを含む平面とが互いに直交するように配置されている。こうすることにより、透明板６７、ダイクロイックミラー６８，６９で発生する非点収差と、偏光ビームスプリッタ５２，５３，５４で発生する非点収差が互いに打ち消し合うように作用する。本実施の形態の構成の最大の特徴は、特に偏光ビームスプリッタ５２，５３，５４の偏光分離ミラーとなるガラス基板と媒質である液体との間に屈折率差を設け、偏光ビームスプリッタ５２，５３，５４が偏光子、及び検光子としての機能と、色合成光学系で発生する非点収差を補正する機能とを併せ持っていることである。
【００５８】
以下に、非点収差発生の原理、非点隔差量について、図５（ａ），（ｂ）に示すモデル図を用いて説明する。
【００５９】
図５（ａ）は、屈折率差を有する境界平面Ａに収束光が斜めに入射する場合である。入射媒質から点Ｑに向かって進む光線が境界平面Ａ上の点Ｂで屈折するものとする。入射側媒質の屈折率をｎ、出射側媒質の屈折率をｎ′、入射角をθ、屈折角をθ′とすると、スネルの法則から、
【００６０】
【数９】

【００６１】
の関係が成り立つ。
【００６２】
入射側媒質中のサジタル近軸光線は、点Ｑから境界平面Ａに下した垂線の足をＮとし、直線ＮＱを中心軸として直線ＢＱを回転してできる円錐の表面上にあると考えてよい。従って、サジタル近軸像点Ｑ_Sは直線ＮＱ上に存在するはずである。
【００６３】
△ＢＮＱと△ＢＮＱ_Sの関係から、
【００６４】
【数１０】

【００６５】
の関係が成り立つ。（数９）、（数１０）から、サジタル近軸像点Ｑ_Sの位置を表す式として、次の式が得られる。
【００６６】
【数１１】

【００６７】
一方、メリディオナル近軸像点を求めるために、入射側媒質から点Ｑに向かい境界面Ａ上の点Ｂ′に入射する入射光線を考える。点Ｂ′は点Ｂからわずかに離れている。点Ｂ′に入射する入射光線の入射角をθ＋δθとし、屈折角をθ′＋δθ′とする。△ＢＢ′Ｑと△ＢＢ′Ｑ_Mに三角形の正弦法則を適用すると、それぞれ、
【００６８】
【数１２】

【００６９】
【数１３】

【００７０】
の関係が成り立つ。（数１２）、（数１３）から、
【００７１】
【数１４】

【００７２】
となる。δθ、δθ′がいずれも非常に小さいとすると、（数１４）は、
【００７３】
【数１５】

【００７４】
となる。（数９）の両辺をθで微分すると、次のようになる。
【００７５】
【数１６】

【００７６】
（数１５）、（数１６）より、δθ′／δθを消去すると、メリディオナル近軸像点Ｑ_Mの位置を表す式として、次式が得られる。
【００７７】
【数１７】

【００７８】
（数１１）、（数１７）の比較から、屈折率差を有する境界平面に光線が斜めに入射する場合、サジタル近軸像点Ｑ_Sとメリディオナル近軸像点Ｑ_Mは一致しないことがわかる。
【００７９】
次に、図５（ｂ）に示すように、平行平面の透明板Ｐが光軸に対して斜めに配置されている場合を考える。透明板Ｐの厚さをｔ、屈折率をｎと、透明板Ｐの外部媒質の屈折率をｎ′とする。
【００８０】
透明板Ｐが無い場合の近軸像点をＱ、光軸に沿って進む光線が透明板Ｐに入射する場合の入射点をＢ、出射点をＣとする。透明板Ｐの入射平面による点Ｑに対応するサジタル近軸像点をＱ_S1、メリディオナル近軸像点をＱ_M1、出射側平面による点Ｑ_S1に対応するサジタル近軸像点をＱ_S2、メリディオナル近軸像点をＱ_M2とする。
【００８１】
（数１１）、（数１７）により、以下の式が成り立つ。
【００８２】
【数１８】

【００８３】
【数１９】

【００８４】
【数２０】

【００８５】
【数２１】

【００８６】
透明板Ｐの厚さｔ、光線の入射角θを用いると、
【００８７】
【数２２】

【００８８】
と表せる。また、図５（ｂ）より、
【００８９】
【数２３】

【００９０】
【数２４】

【００９１】
となり、（数１８）、（数１９）、（数２２）を（数２３）、（数２４）に代入し、その結果を（数２０）、（数２１）に代入すると、次式が得られる。
【００９２】
【数２５】

【００９３】
【数２６】

【００９４】
（数２５）、（数２６）より、透明板Ｐが光軸に対して斜めに配置された場合の近軸像点Ｑに対応する近軸像点Ｑ_S2、Ｑ_M2を求めることができる。透明板Ｐが光軸に対して垂直でない場合には、点Ｑ_S2と点Ｑ_M2は一致しないので非点収差を発生することがわかる。
【００９５】
サジタル近軸像点Ｑ_S2とメリディオナル近軸像点Ｑ_M2の間隔をｄとすると、
【００９６】
【数２７】

【００９７】
となり、（数２５）、（数２６）を（数２７）に代入し、さらに（数９）を利用してθ′を消去すると、非点隔差ｄは次式で求めることができる。
【００９８】
【数２８】

【００９９】
また、媒質が空気の場合、屈折率ｎ′は１とし、（数２８）は次式のように表せる。
【０１００】
【数２９】

【０１０１】
図３に示した構成は、図２（ｂ）に示したモデル図のように透明板６７、ダイクロイックミラー６８，６９、第２レンズ群６４，６５，６６、偏光ビームスプリッタ５２，５３，５４をそれぞれ配置することで、非点収差の補正をしている。この配置方法の中で、特に第２レンズ群６４，６５，６６の効果を図６に示す投写光学系の概略図を用いて説明する。
【０１０２】
尚、ここで、図６に示す、反射型ライトバルブ９１を、図３に示す、反射型ライトバルブ５６に対応するとした場合、図６の偏光ビームスプリッタ９２、第２レンズ群９３、色合成光学系を構成する平行平面板９４，９５，９６は、それぞれ、図３の偏光ビームスプリッタ５３、透明板６７、ダイクロイックミラー６９、６８に対応する。又、図６に示す、第１レンズ群９７は、図３の第１レンズ群７１に対応している。
【０１０３】
反射型ライトバルブ９１からの反射光は、偏光ビームスプリッタ９２、第２レンズ群９３、色合成光学系を構成するダイクロイックミラー、透明板、または平面ミラーとなる平行平面板９４，９５，９６、第１レンズ群９７をそれぞれ通過してスクリーン（図示せず）に投写される。
【０１０４】
実線９８は第２レンズ群９３を用いた場合の光線、破線９９は第２レンズ群９３が無い場合の光線である。
【０１０５】
本実施の形態の投写型表示装置装置は反射型ライトバルブ９１を用い、偏光子、及び検光子として多層膜を利用した偏光ビームスプリッタ９２を用いているため、特に投写画像の周辺のコントラストは偏光ビームスプリッタ９２に入射する光線の入射角に依存する。従って、偏光ビームスプリッタ９２中を通過する光はテレセントリックに近いことが好ましい。
【０１０６】
また、図３に示したように装置全体をコンパクトにするため、反射型ライトバルブ５５，５６，５７からＣＲＴ５８，５９，６０までの光軸は平行であること、即ち、偏光ビームスプリッタ５２，５３，５４の偏光分離面が互いに平行であることが望ましい。そのためには、図６に示すように第１レンズ群９７と反射型ライトバルブ９１との間に偏光分離機能と非点収差補正機能を併せ持つ偏光ビームスプリッタ９２と、色合成光学系として少なくとも３つの平行平面板を配置する空間が必要となる。この場合、投写レンズのバックフォーカスは非常に長いものが要求される。本実施の形態においては、反射型ライトバルブ９１の有効表示領域が対角２．５インチ（縦横比３：４）、投写レンズの焦点距離が約７８ｍｍ、Ｆナンバが４．０のものを用いており、バックフォーカスは空気光路長換算で少なくとも３２０ｍｍ以上、望ましくは３５０ｍｍ以上を必要とする。第１レンズ群９７のみで投写レンズを構成しようとすると、偏光ビームスプリッタ９２を出射した光は破線９９のように進行し、投写レンズの反射型ライトバルブ側のレンズ、および色合成光学系を構成する平行平面板９４，９５，９６は大口径のものが必要となる。従って、投写レンズ、色合成光学系とも非常に高価で、しかも投写レンズは重量の重いものとなる。
【０１０７】
そこで、正パワーを有する第２レンズ群９３を第１レンズ群９７とは十分離れた位置に配置して投写レンズ全体を長い空間を有する２群で構成すれば、実線９８のように光は進行し、投写光学系全体をコンパクトに構成できる。第２レンズ群９３は、材料をプラスチックとして偏光ビームスプリッタ９８から出射する光の有効領域に応じて周辺を長方形状に切断して用いてもよい。
【０１０８】
このように、第２レンズ群９３を、平行平面板９４，９５，９６と偏光ビームスプリッタ９２との間に配置することで、装置全体のコンパクト性とテレセントリック性、及び非点収差補正の機能を同時に満たすことができる。この構成は、偏光ビームスプリッタ９２の代わりに非点収差の補正のみの機能を有する平行平面の透明板を配置する場合の光学装置にも同様に有効である。
【０１０９】
次に、パワーを有する第２レンズ群６４，６５，６６が配置された場合の透明板６７、およびダイクロイックミラー６８、６９で発生する非点収差を、図７に示すモデル図を用いて説明する。なお、光線はスクリーン側から反射型ライトバルブ側に進行するものとして考える。
【０１１０】
図７中の平行平面の透明板Ｐは図３の透明板６７、ダイクロイックミラー６８、６９に、レンズＬは第２レンズ群６４、６５、６６に相当する。
【０１１１】
レンズＬの焦点距離をｆ、レンズＬが無い場合のサジタル近軸像点をＱ_aS、メリディオナル近軸像点をＱ_aM、非点隔差をｄ₁、レンズＬの主平面からサジタル近軸像点Ｑ_aSまでの距離をａとすると、レンズＬによる虚像のサジタル倍率ｍ_S、メリディオナル倍率ｍ_Mは次式で表すことができる。
【０１１２】
【数３０】

【０１１３】
【数３１】

【０１１４】
また、レンズＬが配置された場合のサジタル近軸像点をＱ_bS、メリディオナル近軸像点をＱ_bM、非点隔差をｄ₁′とし、レンズＬの主平面からサジタル近軸像点Ｑ_bSまでの距離をｂ_S、メリディオナル近軸像点Ｑ_bMまでの距離をｂ_Mとすると
【０１１５】
【数３２】

【０１１６】
【数３３】

【０１１７】
【数３４】

【０１１８】
となる。（数３０）、（数３１）、（数３２）、（数３３）、（数３４）より、非点隔差ｄ′は次式で表すことができる。
【０１１９】
【数３５】

【０１２０】
（数３５）はｄ₁がｆ、ａよりも充分小さいとすると次のように近似できる。
【０１２１】
【数３６】

【０１２２】
従って、（数２８）、（数３６）より、図７の透明板Ｐの非点隔差ｄ₁′は、透明板Ｐの板厚をｔ₁、屈折率をｎ₁、媒質の屈折率をｎ₁′、透明板Ｐへの光線入射角をθ₁とすると、次式で求めることができる。
【０１２３】
【数３７】

【０１２４】
一方、図３に示した偏光ビームスプリッタ５２、５３、５４で発生する非点隔差ｄ₂は、偏光分離ミラー基板の板厚をｔ₂、基板の屈折率をｎ₂、液体の屈折率をｎ₂′、液体中から偏光分離面への光線入射角をθ₂とすると、（数２８）により次式となる。
【０１２５】
【数３８】

【０１２６】
非点隔差ｄ₂は液体中での値なので、偏光ビームスプリッタ５２，５３，５４を出射した後の空気中での、即ち空気換算での非点隔差ｄ₂'はｄ₂'＝ｄ₂／ｎ₂’と言う関係から次式のようになる。
【０１２７】
【数３９】

【０１２８】
従って、（数３７）、（数３９）より、図３に示した投写光学系は、次式を満足することで非点収差を補正することができる。
【０１２９】
【数４０】

【０１３０】
（数３７）、（数３９）より、板厚ｔ₁，ｔ₂の関係は次式の条件を満足すればよいことがわかる。
【０１３１】
【数４１】

【０１３２】
なお、図３に示した構成では、色合成光学系の透明板６７、ダイクロイックミラー６８，６９のそれぞれの基板と、偏光ビームスプリッタの偏光分離ミラー基板は、屈折率がいずれも同じものを用いており、ｎ₁＝ｎ₂となり、さらに透明板６７、ダイクロイックミラー６８，６９の媒質は空気であるのでｎ₁′＝１であるので、（数４１）は、
【０１３３】
【数４２】

【０１３４】
となる。
【０１３５】
以上の非点収差の考え方、及び非点収差の補正条件は、投写光学系の光軸上、またはその近くを通る光線を基準にして説明したもので、光軸から離れた位置を通過し、光軸とのなす角度が大きい光線ほど、厳密な非点収差の様子は光軸付近とは若干異なる。しかし、光軸に対して斜めに傾いた平行平面な透明板を、結像性能を有する光が透過した場合に起こる非点収差の基本的な考え方と傾向は同様であり、特に透明板の板厚が比較的薄い場合には光軸上付近と比べて大きな違いとはならない。従って、上記非点収差補正条件は、図３に示したような投写型表示によって投写された投写画像の全有効領域の解像度向上に十分大きな効果がある。
【０１３６】
また、すべての屈折率の値は可視光の中心波長付近であるｅ線（５４６．０７ｎｍ）での値を用いている。屈折率は波長分散特性を有し波長によって若干屈折率が異なり、厳密には、赤、青、緑の３原色光それぞれの条件に応じて最適化すればよい。しかし、可視光の中で最も視感度が高く、投写画像の解像度に支配的に影響する緑色光であるｅ線を基準としても、非点収差補正効果には特に問題とはならない。
【０１３７】
本実施の形態では、第２レンズ群６４，６５，６６の焦点距離ｆが２４０ｍｍ、第２レンズ群の主平面から第２レンズ群６４，６５，６６が無い場合のサジタル近軸像点までの距離ａが１１０ｍｍであり、（数３０）よりサジタル倍率ｍ_Sは約０．６８６となる。また、透明板６７、ダイクロイックミラー６８，６９基板、偏光ビームスプリッタ５２，５３，５４の偏光分離ミラー基板のそれぞれの屈折率ｎ₁は１．５２、偏光ビームスプリッタ５２，５３，５４の液体の屈折率ｎ₂は１．４４、媒質（空気）側から透明板６７、ダイクロイックミラー６８，６９への光線入射角θ₁は４５°、液体側から偏光ビームスプリッタ５２，５３，５４の偏光分離ミラー８４に入射する光線の入射角θ₂は５５．６°であり、（数４２）よりｔ₂／ｔ₁は０．６６８となる。
【０１３８】
ここで、図３に示したダイクロイックミラー６８，６９と平面ミラー７０の光反射面の面精度は、投写光学系の解像度性能に大きく影響し、また、この面精度は基板の板厚条件に大きく左右される。ハイビジョン映像などの高解像度の投写画像と表示する場合、各反射面の面精度は理想的な平面（曲率半径は無限大）に対して面が凹状、または凸状のどちらかに変形しているとして、曲率半径で少なくとも±２λ（λは入射する光の中心波長）以下、望ましくは±λ以下が要求される。
【０１３９】
基板の板厚が薄いと誘電体多層膜を蒸着した際の応力や、装置に組み込んで固定する際の周辺機構部品による圧力の影響で面精度は劣化し易い。本実施の形態のダイクロイックミラー６８，６９と平面ミラー７０の有効領域は、それぞれ少なくとも８０ｍｍ×６０ｍｍ以上を必要とし、表面研磨後も上記面精度の条件のを満たすためには、少なくとも１．５ｍｍ以上、好ましくは２ｍｍ以上の基板厚が必要となる。このうち平面ミラー７０は表面鏡であり、十分な厚さの基板を使用できるので問題ないが、ダイクロイックミラー６８，６９は基板が厚すぎると、投写光学系の光軸から離れた位置を通過する光線の非点収差の補正が困難となる。従って、基板厚は少なくとも３．０ｍｍ以下、好ましくは２．５ｍｍ以下が望ましい。
【０１４０】
以上のことから、ダイクロイックミラー６８，６９の基板厚は１．５ｍｍ以上３．０ｍｍ以下が望ましい。また、偏光ビームスプリッタ５２，５３，５４は、投写光学系の光路中では反射型ライトバルブ５５，５６，５７からの光が透過するのみなので、偏光分離ミラー基板の面精度による解像度劣化の影響はほとんどないと考えてよい。
【０１４１】
従って、本実施の形態では透明板６７とダイクロイックミラー６８，６９の厚さｔ₁を約２．０ｍｍし、（数４２）による計算結果から偏光分離ミラー基板の厚さｔ₂を約１．３ｍｍとしている。こうすることで、投写光学系全体としての非点収差を良好に補正でき、高解像度の投写画像を表示できる。
【０１４２】
上記説明では、色合成光学系の透明板６７、ダイクロイックミラー６８、６９で発生する非点収差を、第２レンズ群（６４，６５，６６）の虚像倍率ｍの２乗分だけ小さくして、しかも、その小さくした非点収差を、偏光ビームスピリッタ（５２，５３，５４）の偏光分離ミラー８４で発生する非点収差により打ち消し合う様に構成する場合等について述べた。
【０１４３】
次に述べるのは、上記実施の形態とは異なり、第２レンズ群を備えず、色合成光学系で発生する非点収差を偏光分離ミラー８４で発生する非点収差により打ち消し合う様に構成する場合の具体例である。
【０１４４】
即ち、この場合、上記（数４２）において、ｍ_s＝１とした場合に相当する。従って、第２レンズ群の虚像倍率がｍ_s＝０．６８６となる上記実施の形態においては、ｔ₂／ｔ₁＝０．６６８が導き出されたが、ここでは、（数４２）はｔ₂／ｔ₁＝０．６６８／０．６８６²＝１．４１９の値となる。
【０１４５】
このことから、ｔ₁＝２．０ｍｍとすると、ｔ₂＝２．８３９ｍｍとなるので、この場合、偏光ビームスプリッタの偏光分離基板の厚さは、２．８４ｍｍとすればよい。
【０１４６】
以下に、図３に示した構成の中で、照明光学系の構成について図８を参照して説明する。図３の構成図では図示していないが、光源４１からの放射光が反射型ライトバルブ５５，５６，５７を照明するまでの光路中には図８のようにリレーレンズ１０５，１０６を配置するとよい。反射型ライトバルブ１０７は図３に示した反射型ライトバルブ５５，５６，５７と同じものである。第１のリレーレンズ１０５と第２のリレーレンズ１０６との間には図３に示したダイクロイックミラー４３，４４，４５で構成される色分解光学系、前置偏光子４６，４７，４８、平面ミラー４９，５０，５１が配置され、第２のリレーレンズ１０６と反射型ライトバルブ１０８の間には偏光ビームスプリッタ５２，５３，５４が配置される。光源４１はランプ１０１と楕円面鏡１０２とで構成され、ランプ１０１はキセノンランプであり、３原色の色成分を含む光を放射する。楕円面鏡１０２はガラス製であり、反射面にアルミニウム薄膜層がコーティングされてある。なお、光反射面には赤外光を透過させ可視光を反射する多層膜を蒸着したものであってもよい。
【０１４７】
ランプ１０１の放射光は楕円鏡１０２で反射され、コールドミラー１０３によって赤外光が除去されて楕円面鏡１０２の第２焦点１０４に集光する。第２焦点１０４を通過した後、発散光となった光は第１のリレーレンズ１０４によって平行に近い光に変換される。誘電体多層膜を用いたダイクッロイックミラーは光線の入射角依存性によって分光性能が変化する特性を持つので、ダイクロイックミラーを通過する光はできるだけ平行光であることが望ましい。平行に近い光は第２のリレーレンズ１０６によって再び集光され反射型ライトバルブ１０７を照明する。リレーレンズ１０５，１０６は楕円面鏡１０２の第２焦点１０３に結像されたランプ１０１の像を反射型ライトバルブ１０７の有効表示用域に対応する拡大倍率で効率よく照明する役割を有する。
【０１４８】
なお、図８では第１のリレーレンズ１０５を２枚構成としているが１枚、または３枚以上であってもよい。また、第２のリレーレンズ１０６は、図３に示した色分解光学系と前置偏光子４６，４７，４８の間、または前置偏光子４６，４７，４８と偏光ビームスプリッタに導く平面ミラー４９，５０，５１の間に配置しても良い。さらに、本実施の形態では、ランプ１０１にキセノンランプを用いたが、他にメタルハライドランプやハロゲンランプなどを用いてもよい。
【０１４９】
以下に、前置偏光子４６，４７，４８の詳細な構成を図９を参照して説明する。
【０１５０】
枠体１１１の内側にはＶ字状の溝が形成され、その溝に偏光選択性ミラー１１４，１１５の端部を挿入し、それぞれの断面がＶ字状になるように配置している。枠体１１１、ガラス基板からなる入射窓１１２と出射窓１１３、偏光分離ミラー１１４，１１５で構成される容器の空間には液体１１６が充填されている。液体材料、及び偏光分離ミラー１１４，１１５の多層膜構成は、図４に示した偏光ビームスプリッタ５２，５３，５４のものと同じものを用いている。
【０１５１】
図９に示すように、前置偏光子４６，４７，４８に垂直に入射する自然光１１７はそれぞれ入射窓１１２、液体１１６を透過して偏光分離ミラー１１４へ５５．６°の角度で入射する。偏光分離ミラー１１４により、自然光１１７はそれぞれＳ偏光成分１１８とＰ偏光成分１１９とに分離され、Ｐ偏光成分１１９は、液体１１６を透過後、出射窓１１３より出射し、Ｓ偏光成分１１８ｂは枠体１１１の内壁にそれぞれ入射する。
【０１５２】
前置偏光子４６，４７，４８のコンパクト性を確保するために、偏光分離ミラー１１４，１１５の枚数は２枚とし、光軸に対してＶ字状に対称に配置している。偏光分離ミラー１１４，１１５によって反射された不要となるＳ偏光成分は出射窓１１３側に進行しないように、Ｖ字の頂点は光源側に向けて配置するとよい。偏光分離ミラーが１枚の場合には、光軸方向の寸法が大きくなるだけでなく、前置偏光子に光が斜めに入射する場合に入射角依存性が非対称になり、この影響が投写画像に現われやすいという問題を生じる。また、３枚以上の偏光分離ミラーを用いてジクザグ状に配置してもよいが、奇数枚の場合、光軸に対して偏光分離ミラーの配置が非対称となるため、偶数枚の構成の方が好ましい。さらに、不要光となるＳ偏光成分が偏光分離ミラーによって反射された後、隣り合った偏光ビームスプリッタに入射し、多重反射光の一部が出射窓側に進行する場合がある。この不要偏光成分が図３に示した偏光ビームスプリタ５２，５３，５４、及び反射型ライトバルブ５５，５６，５７に到達すると投写画像のコントラスト性能を著しく劣化させる要因となる場合があるので注意を要する。このように、図９に示した構成の前置偏光子は、直線偏光に近い光を効率良く取り出せることがわかる。
【０１５３】
前置偏光子と偏光ビームスプリッタと配置関係は、前置偏光子から出射するＰ偏光が偏光ビームスプリッタではＳ偏光として反射されるように配置する。一般に、入射光は光軸を中心に、ある角度範囲に広がっており、入射する光の波長も単一波長ではないことから、Ｓ偏光の反射率は上記入射光の使用条件でも偏光分離ミラーの誘電体多層膜の層数を増やすことで１００％に近づけることが比較的容易であるのに対し、Ｐ偏光の透過率を１００％に近づけることは困難である。従って、不要偏光成分をカットする必要がある前置偏光子ではＰ偏光を取り出すことが好ましい。偏光ビームスプリッタに入射する直線偏光を効率よく反射型ライトバルブ側へ導き、また、黒表示の場合には反射型ライトバルブから反射された読み出し光を偏光ビームスプリッタでカットする必要があるために、偏光ビームスプリッタに入射する偏光成分はＳ偏光であることが好ましい。こうすることにより、高コントラストの投写画像を表示できる。
【０１５４】
図３に示した本発明の投写型表示装置は、第２レンズ群６４，６５，６６を用いているので投写光学系がコンパクトでありながら偏光ビームスプリッタ５２，５３，５４中の通過する光のテレセントリック性が良好という性能を有する。従って、偏光ビームスプリッタの偏光分離面に入射する主光線は、ほぼ投写光学系の光軸とほぼ平行であり、偏光分離面への光線入射角依存性による偏光分離性能の劣化がほとんど発生しない。従って、偏光分離性能の劣化によって生じる投写画像のコントラスト低下や不均一性の問題がない、高画質な投写画像を表示できる。
【０１５５】
また、図３に示した構成は、投写レンズが実質的に１本であるので、カラーシェーディングは発生しない。また、光源４１から各反射型ライトバルブ５５，５６，５７までの照明光路長が３色で等しく、また各反射型ライトバルブ５５，５６，５７の画面中心が投写レンズの光軸上に位置するので、色むらの発生は少ない。
【０１５６】
本実施の形態では、ＣＲＴ画面の水平方向にそれぞれ３つのＣＲＴ、書き込みレンズ、反射型ライトバルブ、偏光ビームスプリッタ、第２レンズ群を配列する構成としたが、ＣＲＴ画面の垂直方向に配列してもよい。
【０１５７】
また、本実施の形態では画像源としてＣＲＴを用いたが、例えば透過型のＴＦＴ液晶パネルを用い、後方からメタルハライドランプなどの光源で照明するようにし、液晶パネル上に映像信号に応じて形成された光学像を書き込みレンズにより反射型ライトバルブの光導電層上に結像させる構成としてもよい。また、書き込み光学系も、書き込みレンズの他にイメージガイドとして用いられる光フィアバーなどを用いてもよい。
【０１５８】
以下に、本発明の他の実施の形態について説明する。
【０１５９】
図１０は、図３に示した投写型表示装置の中で色合成光学系の構成のみが異なる場合の投写光学系の構成図である。
【０１６０】
色合成光学系は、平面ミラー１３０，１３３、ダイクロイックミラー１３１、１３２により構成される。
【０１６１】
反射型ライトバルブ１２１からの光は、偏光ビームスプリッタ１２４、第２レンズ群１２７を透過後、２枚のダイクロイックミラー１３１，１３２を透過して第１レンズ群１３４に入射する。また、反射型ライトバルブ１２２からの光は、偏光ビームスプリッタ１２５、第２レンズ群１２８を透過後、表面鏡に平行平面の透明板を接合した平面ミラー１３０とダイクロイックミラー１３１によって反射され、ダイクロイックミラー１３２を透過して第１レンズ群１３４に入射する。さらに、反射型ライトバルブ１２３からの光は、偏光ビームスプリッタ１２６、第２レンズ群１２９を透過後、表面鏡の平面ミラー１３３とダイクロイックミラー１３２の裏面で反射されて第１レンズ群１３４に入射する。
【０１６２】
平面ミラー１３０，１３３の反射面、ダイクロイックミラー１３１，１３２の色合成面は、投写光学系の光軸に対していずれも４５°傾けて配置している。また、ダイクロイックミラー１３１，１３２の基板、および平面ミラー１３０の反射面と接合している透明板はいずれも図３に示した各種基板のものと同じものを用いている。
【０１６３】
図１０に示す投写光学系の色合成光学系は、平面ミラー１３０とダイクロイックミラー１３２の反射面を事実上裏面反射とすることにより、３つの反射型ライトバルブ１２１，１２２，１２３からそれぞれ出射する光の非点収差補正の条件を同一にしている。
【０１６４】
（数４０）の条件式と、ダイクロイックミラー１３１、１３２の反射面の面精度を考慮し、偏光ビームスプリッタ１２４，１２５，１２６の偏光分離ミラーの基板厚ｔ₂は２ｍｍ、平面ミラー１３０の反射面と接合している透明板の基板厚は０．７５ｍｍ、ダイクロイックミラー１３１，１３２の基板厚はそれぞれ１．５ｍｍとし、色合成光学系における各色毎の平行平面板の総板厚ｔ₁はいずれも３．０ｍｍとなるようにしている。
【０１６５】
この場合、（数４１）の基板厚ｔ₁、ｔ₂はそれぞれ次式で表した値となる。
【０１６６】
【数４３】

【０１６７】
【数４４】

【０１６８】
ただし、ｉは色合成光学系の平行平面板を透過する枚数、ｊは色合成光学系で発生する非点収差を補正するために設けられた平行平面の枚数である。裏面反射の場合は１回の反射につき２枚の平行平面板を透過するものと考える。
【０１６９】
図１０に示した実施の形態は、反射型ライトバルブ１２１，１２２，１２３からのそれぞれの光路について、ｊはいずれも１であるが、ｉについては反射型ライトバルブ１２１からの光路が２、反射型ライトバルブ１２２からの光路が３、反射型ライトバルブ１２３からの光路が２となる。
【０１７０】
このように、図１０に示した実施の形態では光線が複数の平行平面板を透過する場合、及び２回透過する場合と同じ条件となる裏面反射を用いる場合で色合成光学系を構成しているが、非点収差補正の考え方、および補正条件の基本式である（数４０）はそのまま応用できる。
【０１７１】
以上の実施の形態ではライトバルブとして光導電層に書き込まれた画像に応じて読み出し光の偏光状態を液晶層で変調する反射型ライトバルブを用いたが、他の方式の液晶パネルや電気光学結晶を用いるものなど、複屈折性の変化として光学像を形成する反射型のものであればライトバルブとして用いることができる。
【０１７２】
また、本発明の非点収差補正の考え方、及び方法は、透過型のライトバルブの場合や、光変調方式として、散乱、回折、または光偏向方式のライトバルブなど、光学的特性の変化として光学像を形成するものであればすべて応用できる。
【０１７３】
以下、本発明の参考例として、透過型のライトバルブを用いて構成した投写型装置の一実施の形態を図１１を用いて説明する。
【０１７４】
透過型ライトバルブ１５０、１５１、１５２は、ツイスト・ネマティック液晶を光変調材料として用いたＴＦＴ液晶セルと、その前後に偏光子、検光子として用いる偏光板を配置したものである。
【０１７５】
光源１４１から放射される光は、紫外光と赤外光を吸収、または反射し、可視光のみを透過するＵＶ−ＩＲカットフィルタ１４２と平面ミラー１４３を経て、ダイクロイックミラー１４４，１４５と平面ミラー１４６で構成される色分解光学系によって、赤、緑、青の３原色光に分解される。３原色光は、それぞれ対応するフィールドレンズ１４７，１４８，１４９、透過型ライトバルブ１５０，１５１，１５２に順次入射する。
【０１７６】
色合成光学系は、平面ミラー１５３、及びダイクロイックミラー１５４，１５５により構成される。投写レンズは、正パワーを有する第２レンズ群１５６，１５７と第１レンズ群１５８により構成される。また、平面ミラー１５３の反射面、及びダイクロイックミラー１５４，１５５の色合成面は、いずれも投写レンズの光軸に対して４５°に傾けて配置している。
【０１７７】
ライトバルブ１５０，１５１，１５２からの出射光は、色合成光学系によって１つに合成され、投写レンズによってスクリーン上に拡大投写される。
【０１７８】
先述したように、色合成光学系を構成する平面ミラー１５３、ダイクロイックミラー１５４，１５５の光反射面は高い面精度が要求され、面精度は基板厚に大きく左右される。特に、この面精度は反射面の位置が投写レンズの主点に近いほど、投写画像の解像度に及ぼす影響が大きくなる。即ち、平面ミラー１５３、ダイクロイックミラー１５４に比べてダイクロイックミラー１５５の光反射面の面精度の条件が厳しくなる。
【０１７９】
そこで、図１１に示す構成は、第１レンズ群１５８とは離れた位置にある第２レンズ群１５６，１５７をそれぞれ平面ミラー１５３、ダイクロイックミラー１５４とダイクロイックミラー１５５との間に配置している。こうすることにより、（数３６）からわかるように、ライトバルブ１５０，１５１，１５２側で見たダイクロイックミラー１５５で発生する非点隔差は、第２レンズ群１５６が無い場合と比べて、正パワーを有する第２レンズ群による虚像倍率の２乗分だけ小さくすることができる。従って、ダイクロイックーミラー１５５の基板厚は、第２レンズ群１５６が無い場合よりも厚くすることができ、非点収差を大きくすることなくダイクロイックミラー１５５の反射面を高い面精度とすることができる。
【０１８０】
図１１に示した実施の形態は、色合成光学系で発生する非点収差を投写光学系の近軸上で完全に補正するものではないが、本発明の光学装置の非点収差の考え方は同じであり、第２レンズ群１５６を用いる効果は大きい。
【０１８１】
尚、第２レンズ群１５７を通過する光路では、ライトバルブ１５２を出射する光が平面ミラー１５３、ダイクロイックミラー１５５によって反射されるのみなので、非点収差を発生させる要因がない。従って、第２レンズ群１５７は非点収差を低減すると言う効果は発揮しない。しかし、第１レンズ群１５８と、第２レンズ群１５６、１５７は、一体で結像性能を有するレンズ系であるため、結像性能上第２レンズ群１５７は必要である。
【０１８２】
又、図１１の構成においても、ライトバルブ１５０，１５１，１５２から第１レンズ群１５８までの間に、平行平面の法線と投写レンズの光軸とを含む平面と、ダイクロイックミラー１５４，１５５の色合成面の法線と投写レンズの光軸とを含む平面が互いに直交するような透明板を配置する空間を設けて、非点収差を補正してもよい。
【０１８３】
以上、図１１に示した参考例では、透過型のライトバルブを用いたが、色合成光学系を有する投写光学系を用いるものであれば、反射型のライトバルブを用いた場合でも同様の効果が得られる。
【０１８４】
以上のように本発明によれば、色合成光学系で発生する非点収差を良好に補正することができ、しかも投写光学系をコンパクトに構成できる。従って、本発明の光学装置を投写型表示装置に用いることにより、色合成光学系を有し、１つの投写レンズで構成した投写光学系の場合でも、非常に高い解像度の投写画像を表示でき大きな効果がある。
【０１８５】
尚、上記実施の形態では、フルカラーの投写画像を得るために、ライトバルブを赤用、緑用、青用として３つ用いる投写型表示装置等あるいは、その様な装置に利用する光学補正方法について説明したが、これに限らず例えば、単色光の光学像を形成して出力する光学装置あるいは、この様な光学装置に利用する光学補正方法であってもよい。
【０１８６】
又、上記実施の形態では、本発明の第２レンズ手段としての第２レンズ群と、本発明の偏光分離手段の透明基板としての偏光分離ミラーとを備え、本発明の平面板部材としての、色合成光学系のダイクロイックミラーなどで発生する非点収差を小さくして（あるいは、非点収差を大きくすることなく、ダイクロイックミラーの面精度を上げて）、しかも、その非点収差を打ち消し合う様に補正する場合の投写型表示装置あるいは、その様な装置に利用する光学補正方法について説明した。一方、本発明の参考例としては、例えば、偏光分離手段の透明基板を備えず、第２レンズ手段を備えた構成の装置や、この様な構成の装置に利用する光学補正方法でもよい。この場合、上述した（数３６）からわかる様に、例えば、図３に示した色合成光学系の透明板６７、ダイクロイックミラー６８、６９で発生する非点収差を、第２レンズ群（６４，６５，６６）の虚像倍率ｍの２乗分だけ小さく出来ると言う効果を発揮する。あるいはこれとは別の効果として、非点収差を大きくすることなく、ダイクロイックーミラーの基板厚を、第２レンズ群が無いとした場合に比べて、より一層厚くすることができるので、ダイクロイックミラーの反射面を高い面精度に出来ると言う効果も有している。
【０１８７】
又、上記実施の形態では、本発明の偏光分離手段が、偏光選択特性を有する膜が形成された、所定厚みの透明基板を有している場合について説明した。一方、本発明の参考例としては、これに限らず例えば、偏光分離手段は、偏光選択特性を有する薄膜を備え、その薄膜の両側をプリズム状の部材により保持した構成であってももちろよい。この場合でも、例えば、図３に示した色合成光学系の透明板６７、ダイクロイックミラー６８、６９で発生する非点収差を、第２レンズ群（６４，６５，６６）の虚像倍率ｍの２乗分だけ小さく出来ると言う効果を発揮する。
【０１８８】
本発明の光学補正方法による光学装置の利点は以上明らかなように、色合成光学系で発生する非点収差を良好に補正することができ、しかも投写光学系をコンパクトに構成できることである。従って、本発明の光学装置を用いた投写型表示装置は色合成光学系を有する１つの投写レンズで構成した場合でも、非常に高い解像度の投写画像を表示できる。
【０１８９】
【発明の効果】
以上述べたところから明らかなように本発明は、非点収差を従来に比べてより一層良好に補正することができると言う長所を有する。又、本発明は、従来に比べてより一層高解像度の投写画像を表示できると言う長所を有する。
【図面の簡単な説明】
【図１】本発明の一実施の形態における非点収差を説明する概略図
【図２】（ａ）：本実施の形態における、互いに入射面が直交する２つの平行平面の透明板Ｐ１、Ｐ２を配置した非点収差補正方法を説明する概略構成図
（ｂ）：本実施の形態における、第１レンズ群Ｌ１と、色合成光学系のダイクロイックミラーとなる平行平面の透明板Ｐ１と、第２レンズ群Ｌ２と、透明板Ｐ１で発生する非点収差を補正するような平行平面の透明板Ｐ２と、ライトバルブＬＶとを配置した構成により、非点収差補正方法を説明する概略構成図
【図３】本発明の投写型表示装置の一実施の形態の構成を示す斜視図
【図４】本実施の形態の偏光ビームスプリッタの構成を示す断面図
【図５】（ａ）：本実施の形態における、屈折率差を有する境界平面Ａに収束光が斜めに入射する場合の、非点収差の原理を説明する説明図
（ｂ）：本実施の形態における、平行平面の透明板Ｐが光軸に対して斜めに配置されている場合の、非点収差の原理を説明する説明図
【図６】本発明の光学装置の一実施の形態の投写光学系の概略構成図
【図７】本実施の形態における、非点隔差量を説明する説明図
【図８】本発明の光学装置の一実施の形態の照明光学系の概略構成図
【図９】本発明の光学装置の一実施の形態の前置偏光子の構成を示す断面図
【図１０】本発明の他の実施の形態における光学装置の投写光学系の概略構成図
【図１１】 本発明の参考例における光学装置の概略構成図
【図１２】反射型ライトバルブの基本構成を示す概略断面図
【図１３】従来の光学装置の構成例を示す斜視図
【符号の説明】
４１ 光源
４３，４４，４５，６８，６９ ダイクロイックミラー
４６，４７，４８ 前置偏向子
４９，５０，５１，７０ 平面ミラー
５２，５３，５４，９２ 偏光ビームスプリッタ
５５，５６，５７，９１ 反射型ライトバルブ
５８，５９，６０ ＣＲＴ
６１，６２，６３ 書き込みレンズ
Ｌ２，６４，６５，６６，９３ 第２レンズ群
Ｐ，Ｐ１，Ｐ２，６７，９４，９５，９６ 透明板
Ｌ１，７１，９７ 第１レンズ群[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical device, an optical correction method, and a projection display device that can be used in an apparatus that magnifies and projects an optical image formed on, for example, a light valve on a screen.
[0002]
[Prior art]
In order to obtain a large screen image, a method of forming an optical image corresponding to a video signal on a light valve, irradiating the optical image with light, and enlarging and projecting the image on a screen by a projection lens is well known. Recently, a projection display device using a liquid crystal panel as a light valve has attracted attention.
[0003]
In order to increase the resolution of a projected image, a method using a reflective light valve capable of increasing the number of pixels without reducing the pixel aperture ratio of a liquid crystal panel, for example, Ledebuhr et al., US Pat. No. 4,836,649 Proposed in the specification. In the case of a reflective light valve, there is no need to provide a switching element between pixel electrodes, so the pixel pitch can be reduced, the density can be easily increased, and a brighter and higher-resolution projection image can be obtained compared to the transmissive type. It is done.
[0004]
A basic configuration example and operation principle of the reflective light valve will be described below with reference to FIG. Between the two transparent electrodes 2 and 6 formed on the two glass substrates 1 and 7, a photoconductive layer 3, a light reflecting layer 4, and a liquid crystal layer 5 as a light modulation layer are sandwiched, and the two transparent electrodes 2. , 6 is applied with a voltage. Write light 8 from the image source enters the photoconductive layer 3 from the glass substrate 1 side. On the other hand, the readout light 9 enters the liquid crystal layer 5 from the glass substrate 7 side. The liquid crystal layer 5 modulates the readout light 9 by changing the applied voltage according to the written image formed on the photoconductive layer 3. The modulated readout light 9 is reflected by the light reflecting layer 4 and then projected on a screen (not shown) as a projected image. As a material for the light modulation layer, ferroelectric liquid crystal, nematic liquid crystal, or the like can be used.
[0005]
Next, FIG. 13 shows a configuration example of a projection display device that uses three reflective light valves for red, green, and blue in order to obtain a full-color, high-brightness, high-resolution projection image. Near-parallel light emitted from the light source 11 passes through a cold mirror 12 that transmits ultraviolet light and infrared light and reflects visible light, and then is green by a color separation optical system including dichroic mirrors 13 and 14 and a plane mirror 15. It is decomposed into light of three primary colors, blue and red. The three primary color lights are incident on the corresponding polarization beam splitters 19, 20, and 21 by the plane mirrors 16, 17, and 18, respectively, and are separated into a reflected S-polarized component and a transmitted P-polarized component. The light enters the corresponding reflective light valves 22, 23, and 24, respectively. The reflection type light valves 22, 23, and 24 modulate the readout light by utilizing the birefringence of the liquid crystal, and have a configuration as shown in FIG. Write light from an image source 25, 26, 27 such as a CRT is imaged on the photoconductive layers of the reflection type light valves 22, 23, 24 by write lenses 28, 29, 30 and an applied voltage corresponding to this write image. As a result, the birefringence of the liquid crystal layer changes. That is, when linearly polarized light having a predetermined polarization direction enters as readout light, the reflected light becomes elliptically polarized light. Accordingly, the S-polarized component is partially converted into the P-polarized component by the reflection type light valves 22, 23, and 24 and is incident on the polarizing beam splitters 19, 20, and 21 again. The P-polarized component contained in the reflected light is transmitted through the polarizing beam splitters 19, 20, 21, and then combined into one by a color combining optical system including dichroic mirrors 31, 32 and a plane mirror 33 and enters the projection lens 34. , S-polarized components are reflected by the polarization beam splitters 19, 20, 21 and travel toward the light source 11. In this way, the optical image formed as a change in birefringence on the liquid crystal layers of the reflective light valves 22, 23, 24 is enlarged and projected on a screen (not shown) by the projection lens 34.
[0006]
[Problems to be solved by the invention]
In the configuration shown in FIG. 13, there is one projection lens 34, which is advantageous in terms of convergence adjustment and color uniformity of the projection images of the three primary colors and compactness of the set as compared with the case where three projection lenses are used. is there. However, a color synthesis optical system for synthesizing the reflected light from the three light valves into one is required, and the color synthesis surfaces of the dichroic mirrors 31 and 32 used in this case are in relation to the optical axis of the projection lens 34. It is arranged obliquely. If a plane-parallel plate (dichroic mirror) having a specific thickness inclined obliquely is in the optical path of the imaging optical system, astigmatism occurs, which causes a significant deterioration in the resolution of the projected image.
[0007]
Therefore, the following two methods are conceivable as means for reducing or eliminating astigmatism generated in the dichroic mirrors 31 and 32.
[0008]
a) Decrease the substrate thickness of the dichroic mirror.
[0009]
b) A dichroic prism that does not generate astigmatism is used.
[0010]
Since the color synthesis optical system is arranged between the light valve and the projection lens, it must be considered as a part of the projection optical system. In that case, the reflective surface of the dichroic mirror in particular requires high surface accuracy, and the substrate thickness The thinner this is, the more difficult it becomes. In particular, when a high-definition projected image such as a high-definition image is displayed, at least a substrate thickness of 1.5 mm or more is required to satisfy the surface accuracy required for the reflecting surface of the dichroic mirror. Therefore, the method a) has a limit, and there is a problem that it is difficult to reduce the adverse effect of astigmatism on the resolution.
[0011]
In the method b), two glass prisms are used as dichroic prisms, and a color composition surface is formed on the joint surface thereof. A method is conceivable in which a liquid having a ratio is filled to form a prism as a whole. However, the former is very expensive and the weight is heavy. In the latter, the optical path length occupied by the liquid in the color synthesis optical path is very long. Therefore, the focus shift of the projected image due to the temperature dependence of the liquid refractive index is difficult. There was a problem that it was difficult to adopt any of them because they could not be ignored.
[0012]
In view of such a conventional problem, the present invention provides an optical device and an optical correction method capable of correcting astigmatism generated in a color synthesis optical system even better than before, and An object of the present invention is to provide a projection display device that can display a projected image with a higher resolution than in the prior art by using this optical device.
[0013]
[Means for Solving the Problems]
  According to a first aspect of the present invention, there is provided image forming means for forming an optical image;
  First lens means disposed forward on the optical axis of the image forming means;
  A second lens unit disposed between the image forming unit and the first lens unit and having a positive power;
  Arranged between the first lens means and the second lens means for color synthesis;Means to transmit the optical imageA first planar plate member;
  Arranged between the second lens unit and the image forming unit and having polarization separation performance.And transmit the optical image.A second planar plate member,
  The first lens unit and the second lens unit are on the image forming unit.Optical imageAre combined so that they can be enlarged and projected on the screen.
  The second flat plate member is a transparent substrate having a predetermined thickness provided with a thin film having polarization selection characteristics on one side and having polarization separation performance,
  The first and second planar plate members are disposed obliquely with respect to the optical axis formed by the first and second lens means,
  A plane including a normal to the plane of the first plane plate member and an optical axis of the first and second lens means; a normal to the plane of the second plane plate member; and the first and second The plane including the optical axis of the lens means is orthogonal to each other,
  Plate thickness t of the first flat plate member₁And the thickness t of the second flat plate member₂Is an optical device characterized by satisfying the following expression.
[Expression 4]

  Where m_SIs the virtual image magnification at the sagittal paraxial image point of the second lens means, n₁Is the refractive index of the first planar plate member, n₁′ Is the refractive index of the medium of the first flat plate member, θ₁Is the incident angle of the light beam on the optical axis of the first and second lens means that enters the flat plate member from the medium of the first flat plate member, n₂Is the refractive index of the second planar plate member, n₂′ Is the refractive index of the medium of the second flat plate member, θ₂Is the incident angle of the light beam on the optical axis of the first and second lens means that enters the second flat plate member from the medium of the second flat plate member.
[0014]
  According to a fifth aspect of the present invention, there is provided an image forming means for forming an optical image, a first lens means disposed on the optical axis of the image forming means, the image forming means and the first lens means. Between the second lens means having positive power and between the first lens means and the second lens means, and for color synthesis.Means to transmit the optical imageIt is disposed between the first plane plate member, the second lens means and the image forming means, and has polarization separation performance.And transmit the optical image.A second planar plate member, wherein the first lens means and the second lens means are on the image forming means.Optical imageAnd the second flat plate member is a transparent substrate having a predetermined thickness and provided with a thin film having a polarization selection characteristic on one side, and having a polarization separation performance. The first and second planar plate members are optical correction methods for an optical device disposed obliquely with respect to the optical axis formed by the first and second lens means,
  A plane including a normal to the plane of the first plane plate member and an optical axis of the first and second lens means; a normal to the plane of the second plane plate member; and the first and second The planes including the optical axis of the lens means are orthogonal to each other, and astigmatism caused by the first plane plate member and the second plane plate member is corrected with respect to each other. Thickness t of face plate member₁And the thickness t of the second flat plate member₂Is adjusted so as to satisfy the following expression:
[Expression 4]

  Where m_SIs the virtual image magnification at the sagittal paraxial image point of the second lens means, n₁Is the refractive index of the first planar plate member, n₁′ Is the refractive index of the medium of the first flat plate member, θ₁Is the incident angle of the light beam on the optical axis of the first and second lens means that enters the flat plate member from the medium of the first flat plate member, n₂Is the refractive index of the second planar plate member, n₂′ Is the refractive index of the medium of the second flat plate member, θ₂Is the incident angle of the light beam on the optical axis of the first and second lens means that enters the second flat plate member from the medium of the second flat plate member.
[0015]
  A seventh aspect of the present invention is a light source that emits light including color components of three primary colors;
  Color separation means for separating the emitted light of the light source into three primary color lights;
  Three pre-polarizers on which each of the three output lights of the color separation means is individually incident;
  A plurality of image forming means for forming an optical image as a change in birefringence;
  A polarization separation unit that is provided for each of the image forming units and separates polarization components whose polarization planes are orthogonal to each other;
  Transmitting light from the polarized light separating means provided for each polarized light separating means,Regular partyA second lens having a
  Color synthesizing means for synthesizing light from each of the polarization separating means into one;
  A first lens that emits the light emitted from the color synthesizing unit.
  Each of the polarization separation means is a parallel plane arranged obliquely with respect to the optical axis of the first lens., Transmit the optical imageA dielectric multilayer film having a polarization selectivity is formed on the transparent substrate,
  The color composition meansFor two of the three primary color lights,A parallel plane arranged oblique to the optical axis of the first lens.,A dielectric multilayer film having wavelength selectivity is formed on a transparent substrate.In addition, the two lights that transmit the two lights respectively.It is constructed including an ichroic mirror,The remaining one of the three primary color lights is subjected to antireflection treatment on both surfaces of a parallel flat transparent substrate disposed obliquely with respect to the optical axis of the first lens. It is configured including an optical correction plate that transmits light,
  The first lenses and the second lenses are on the image forming unit.Optical imageAre combined so that they can be enlarged and projected on the screen.
  Of the three primary color lights, the color composition means for the two lightsNormal line of dielectric multilayer film forming surface of each dichroic mirrorOr the normal line of the antireflection surface of the optical correction plate of the color synthesizing means for the remaining one of the three primary color lightsA plane including the optical axis of the first lens and the second lens, a plane including the normal line of the dielectric multilayer film forming surface of each polarization separating means, and the optical axes of the first lens and the second lens Are orthogonal to each other,
  Of the three primary colorsOf these, the thickness of the dichroic mirror of the color synthesizing means for the two lights, and the thickness of the optical correction plate of the color synthesizing means for the remaining one of the three primary color lights Thicknesst₁And the thickness t of the transparent substrate of the polarization separation means corresponding to the three primary color lights₂Is a projection display device that satisfies the following conditions.
[Expression 4]

  Where m_SIs the virtual image magnification at the sagittal paraxial image point of the second lens, n₁Is the dichroic mirror substrateOr the optical correction plateThe refractive index of n₁′ Is the dichroic mirrorOr the optical correction plateThe refractive index of the medium, θ₁Is the dichroic mirror from the mediumOr the optical correction plateThe incident angle of light on the optical axis of the first lens or the second lens,₂Is the refractive index of the transparent substrate of the polarization separation means, n2 'is the refractive index of the medium of the polarization separation means, θ₂Is an incident angle of a light beam on the optical axis of the first lens or the second lens, which enters the polarization separation surface of the polarization separation means from the medium.
[0024]
With the configuration as described above, it is possible to satisfactorily correct, for example, astigmatism generated in the color synthesis optical system, and to make the projection optical system compact. Therefore, the projection display device using the optical device of the present invention can display a projected image with a very high resolution even when the projection display device is constituted by, for example, one projection lens having a color synthesis optical system.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
[0026]
Astigmatism due to the dichroic mirror as the color synthesizing means, as shown in FIG. 1, when the convergent light is transmitted through the transparent flat plate P inclined obliquely with respect to the optical axis, the transparent plate P and the medium ( In this case, the plane including the normal of the boundary with the air) and the principal ray O of the convergent light is defined as the incident plane, and the rays in the plane perpendicular to the incident plane are the sagittal rays S and parallel to the incident plane. If a light ray in a plane is a meridional ray M, the point at which the sagittal ray S and the meridional ray M that have passed through the transparent plate P intersect with the principal ray O is Q._S, Q_MIs caused by different things. In addition, point Q in this case_SAnd point Q_MThe interval is called astigmatic difference.
[0027]
As shown in FIG. 2A, when two parallel flat transparent plates P1 and P2 whose incident surfaces are orthogonal to each other are arranged, the sagittal ray and the meridional ray defined by the transparent plates P1 and P2 are interchanged with each other. Astigmatism also acts to cancel each other. When there is no lens system having power between the transparent plate P1 and the transparent plate P2, astigmatism can be corrected by making the tilt angle with respect to the optical axis, the plate thickness, and the refractive index of the transparent plate the same.
[0028]
However, when a transparent plate for correcting astigmatism is added between the projection lens as the projection means and the light valve as the image formation means in addition to the dichroic mirror as the color synthesis means, the projection lens is very Need to have a long back focus.
[0029]
Therefore, as shown in FIG. 2B, the projection lens is configured by the first lens group L1 and the second lens group L2 having a long air interval, and is interposed between the first lens group L1 and the second lens group L2. A parallel plane in which a color combining optical system is disposed and in which astigmatism generated on a parallel plane transparent plate P1 serving as a dichroic mirror of the color combining optical system is further corrected between the second lens unit L2 and the light valve LV. If the transparent plate P2 is disposed, a projection lens having a small lens outer diameter can be realized while realizing a substantially long back focus (interval from the first lens unit L1 to the light valve LV).
[0030]
In this case, since the second lens group L2 having power is disposed between the color synthesis optical system and the transparent plate P2 that corrects astigmatism generated in the transparent plate P1 of the color synthesis optical system, color synthesis is performed. Astigmatic difference d generated in the optical system₁'Is represented by the following equation.
[0031]
[Formula 6]

[0032]
Where m is the virtual image magnification of the second lens unit L2, and d₁Is an astigmatic difference generated in the color synthesizing optical system in the absence of the second lens unit L2.
[0033]
Therefore, the astigmatic difference generated in the transparent plate P2 disposed between the second lens unit L2 and the light valve LV is d.₂Then, as for the relationship between the transparent plate P1 and the transparent plate P2 for correcting astigmatism, the thickness of each other may be set so as to satisfy the following conditions.
[0034]
[Expression 7]

[0035]
Furthermore, the optical device of the present invention uses a polarization beam splitter as a polarization separation means having functions of a polarizer and an analyzer, and the polarization beam splitter is disposed between the second lens group and the imaging plane. A parallel flat transparent plate that forms the polarization separation surface is arranged so as to correct astigmatism generated in the color synthesis optical system. By doing so, the polarization beam splitter can have a polarization separation function and an astigmatism correction function at the same time.
[0036]
As can be seen from (Equation 6), the astigmatic difference d generated in the transparent plate P1 (dichroic mirror) of the color synthesis optical system.₁′ Is the astigmatic difference d when the second lens unit L2 is not provided.₁As compared with, the square of the virtual image magnification m by the second lens group having positive power can be reduced. A specific embodiment of this point will be described later.
[0037]
A specific embodiment of a projection display device using the optical device of the present invention will be described below with reference to the configuration diagram shown in FIG.
[0038]
The second lens groups 64, 65, and 66 are joined to the corresponding polarization beam splitters 52, 53, and 54, respectively. The first lens group 71 and the second lens groups 64, 65, 66 constitute a projection lens, and the optical system from the polarization beam splitters 52, 53, 54 to the first lens group 71 is a reflective light valve 55. , 56 and 57 are called projection optical systems that project the optical images on the screen.
[0039]
The light emitted from the light source 41 emits light including color components of the three primary colors. The cold mirror 42 reflects visible light and transmits infrared light. The radiated light from the light source 41 is reflected only by the cold mirror 42 and is sequentially decomposed into three primary color lights of green, blue and red by a color separation optical system composed of three dichroic mirrors 43, 44 and 45. Is done. Each primary color light is incident on the front polarizers 46, 47, and 48, respectively, and is emitted as substantially linearly polarized light. Each primary color light that has become substantially linearly polarized light passes through mirrors 49, 50, 51 as incident light and enters the polarization beam splitters 52, 53, 54, and is reflected to the reflective light valves 55, 56, 57 side. The reflective light valves 55, 56, and 57 have the same basic configuration as that shown in FIG.
[0040]
On the other hand, the images formed on the CRTs 58, 59, 60 are imaged on the photoconductive layers of the corresponding reflective light valves 55, 56, 57 by the writing lenses 61, 62, 63 as writing light. The liquid crystal layer, which is a light modulation layer, modulates the incident linearly polarized readout light into elliptically polarized light according to the image formed on the photoconductive layer. The modulated readout light is reflected by the light reflecting layers of the reflection type light valves 55, 56, and 57 and is incident on the polarization beam splitters 52, 53, and 54 again. The reflected polarization component travels toward the light source 41 and is transmitted. The polarized component to be incident on the second lens group 65, 66, 67.
[0041]
The emitted light from the second lens group 65, 66, 67 is combined into one light by a color combining optical system that combines the transparent plate 67, the dichroic mirrors 68, 69, and the plane mirror 70, and the combined light is the first light. The light enters one lens group 71. The optical images on the three reflection type light valves 55, 56, 57 are enlarged and projected on a screen at a position separated by the first lens group 71 and the second lens group 64, 65, 66.
[0042]
The transparent plate 67 is inserted in order to make the astigmatic difference generated in each color combining optical system of the three primary color lights the same. Accordingly, there is an effect that the thicknesses of the transparent plates of the three polarizing beam splitters 52, 53, and 54 can be made the same.
[0043]
The polarization beam splitters 52, 53, and 54, the second lens groups 64, 65, and 66, the transparent plate 67, the dichroic mirrors 68 and 69, the mirror 70, and the first lens group 71 are all preferably housed in one lens barrel. Thus, the projection optical system from the polarization beam splitters 52, 53, 54 to the first lens group 71 can be assembled with high accuracy.
[0044]
Next, a detailed configuration of the polarization beam splitter will be described with reference to FIG. The polarization beam splitters 52, 53, and 54 and the second lens groups 64, 65, and 66 are the same as the polarization beam splitters 52, 53, and 54, and the second lens groups 64, 65, and 66 shown in FIG.
[0045]
The space of the container constituted by the frame 81, the transparent plates 82 and 83, and the polarization separation mirror 84 is filled with a liquid 85. The polarization separation mirror 84 is obtained by vapor-depositing a dielectric multilayer film on a transparent glass substrate. The dielectric multilayer film surface serving as a polarization separation surface is in close contact with the surrounding liquid 85 and exhibits polarization separation performance.
[0046]
The liquid 85 used for the polarization beam splitters 52, 53, and 54 is required to be transparent, to have uniform optical characteristics, to have a low freezing point, to have a high boiling point, and to be inexpensive. In the present embodiment, a liquid mixture that satisfies the above conditions is a three-component liquid mixture of 55% by weight of ethylene glycol, 30% by weight of diethylene glycol, and 15% by weight of glycerin. These three kinds of mixed liquids have good optical performance, and have a freezing point of −52 ° C. and a boiling point of + 198 ° C., and can be used without any problem in the use environment of the projection display apparatus of the present embodiment. Further, the cost is low, and both weight and cost are overwhelmingly advantageous as compared with the case where a glass prism is used.
[0047]
As the liquid, ethylene glycol as a main component and the mixing ratio of the three kinds of liquids may be changed, or pure ethylene glycol or an aqueous ethylene glycol solution may be used. However, when the material of the frame body 91 is aluminum, attention should be paid to the fact that aluminum oxide is precipitated due to the reaction between aluminum and water, and the liquid gradually becomes cloudy. Further, as the liquid, a material that is liquid at the time of assembly but becomes a solid or a gel after completion of the assembly (for example, Shin-Etsu Chemical Co., Ltd. gel transparent silicone resin KE1051) may be used.
[0048]
The polarization selective mirror 84 is formed by depositing a dielectric multilayer film in which low refractive index film layers and high refractive index film layers are alternately laminated on a glass substrate, and is a Brewster that maximizes the transmittance of P-polarized light. A type utilizing the interference effect between the corner and the dielectric multilayer film is adopted. This type of polarization separation mirror is used to change the refractive index of an external medium to n_M, The refractive index of the low refractive index layer is n_L, N is the refractive index of the high refractive index layer_HThen, the optimal incident angle θ of the light beam_MIs obtained by the following equation.
[0049]
[Equation 8]

[0050]
If the condition of (Equation 8) is satisfied, the reflectance of S-polarized light can be increased by increasing the number of layers of the dielectric multilayer film while maintaining the transmittance of P-polarized light at 100%.
[0051]
The polarization separation mirror 84 of the present embodiment uses magnesium fluoride (refractive index 1.39) as a low refractive index film and titanium dioxide (refractive index 2.30) as a high refractive index film. Since the refractive index is 1.44, the optimal light incident angle is 55.6 ° from (Equation 8). Accordingly, the polarization selective mirror 84 is disposed so as to be inclined so that the angle formed with the optical axis of the projection optical system is 34.4 °. The dielectric multilayer film has a 13-layer structure, and each film thickness of the dielectric multilayer film is set so that the S-polarized light reflectance peak becomes the center wavelength of each of the three primary color lights incident thereon.
[0052]
Thus, the reflectance is related to the number of layers of the dielectric multilayer film, and the center wavelength of the reflection wavelength is related to the thickness of each dielectric multilayer film.
[0053]
Further, there are the following two configurations for widening the reflection wavelength band.
[0054]
That is, as a first configuration, the polarization separation mirror 84 is configured by forming a first dielectric multilayer film and a second dielectric multilayer film, each having a different reflection wavelength band of the S-polarized component, on both surfaces of the glass substrate. If so, the reflection wavelength band of S-polarized light can be broadened as a whole. By doing so, even when the wavelength band of the light incident on the polarization beam splitters 52, 53, and 54 is wide, good polarization separation performance can be exhibited.
[0055]
As a second configuration, the polarization separation mirror 84 can widen the wavelength band for reflecting S-polarized light as the refractive index difference between the low refractive index layer and the high refractive index layer constituting the dielectric multilayer film increases. . In the polarization separation mirror 84 of this embodiment, in order to widen the reflection wavelength band of the S-polarized component as much as possible, magnesium fluoride, which is the lowest refractive index material that can be used as a transparent and excellent material, and the highest refraction Although titanium dioxide which is an index material is used, a thin film material having another refractive index may be used. For example, silicon dioxide (refractive index 1.46), dialuminum trioxide (refractive index 1.62), etc. as a low refractive index layer, and zinc sulfide (refractive index 2.30), cerium dioxide (high refractive index layer). A refractive index of 2.30), zirconium dioxide (refractive index of 2.05), tantalum pentoxide (refractive index of 2.10), hafnium dioxide (refractive index of 2.00), or the like can be used. However, in this case as well, the arrangement angle of the polarization separation mirror 84 needs to be set so as to satisfy the condition of (Equation 8).
[0056]
As shown in FIG. 4, the S-polarized light 86 incident perpendicularly to the transparent plate 82 passes through the liquid 85 and enters the polarization separation mirror 84 at an angle of 55.6 °. The S-polarized light 87 reflected by the polarization separation mirror 84 passes through the liquid 85 and is emitted from the transparent plate 83 to the reflective light valve side. The light reflected by the reflective light valve passes through the transparent plate 83 and the liquid 85 again and enters the polarization separation mirror 84. The P-polarized light 88 modulated by the reflection type light valve sequentially passes through the polarization separation mirror 84, the liquid 85, and the second lens group 88, and proceeds to the first lens group 71 side shown in FIG. The light is again reflected to the transparent substrate 82 side by the polarization separation mirror 84.
[0057]
In the configuration shown in FIG. 3, the normal lines and projections of the antireflection surface of the transparent plate 67 and the color synthesis surfaces of the dichroic mirrors 68 and 69 constituting the color synthesis optical system as shown in FIG. The plane including the optical axis of the optical system and the plane including the normal line of the polarization separation surface of the polarization beam splitters 52, 53, and 54 and the optical axis of the projection optical system are arranged to be orthogonal to each other. By doing so, the astigmatism generated in the transparent plate 67 and the dichroic mirrors 68 and 69 and the astigmatism generated in the polarization beam splitters 52, 53, and 54 act so as to cancel each other. The greatest feature of the configuration of the present embodiment is that a difference in refractive index is provided between the glass substrate serving as the polarization separation mirror of the polarization beam splitters 52, 53, and 54 and the liquid as the medium. , 54 has both a function as a polarizer and an analyzer and a function of correcting astigmatism generated in the color synthesis optical system.
[0058]
Hereinafter, the principle of astigmatism generation and the amount of astigmatism will be described with reference to the model diagrams shown in FIGS.
[0059]
FIG. 5A shows a case where convergent light is incident on the boundary plane A having a refractive index difference obliquely. It is assumed that a ray traveling from the incident medium toward the point Q is refracted at a point B on the boundary plane A. Assuming that the refractive index of the incident side medium is n, the refractive index of the outgoing side medium is n ′, the incident angle is θ, and the refractive angle is θ ′, from Snell's law,
[0060]
[Equation 9]

[0061]
The relationship holds.
[0062]
The sagittal paraxial ray in the incident-side medium may be considered to be on the surface of a cone formed by rotating the straight line BQ around the straight line NQ with the perpendicular foot extending from the point Q to the boundary plane A as N. . Therefore, the sagittal paraxial image point Q_SShould be on the straight line NQ.
[0063]
△ BNQ and △ BNQ_SFrom the relationship
[0064]
[Expression 10]

[0065]
The relationship holds. From (Equation 9) and (Equation 10), the sagittal paraxial image point Q_SAs an expression representing the position of the following, the following expression is obtained.
[0066]
## EQU11 ##

[0067]
On the other hand, in order to obtain the meridional paraxial image point, consider an incident light ray that enters the point B ′ on the boundary surface A from the incident side medium toward the point Q. Point B ′ is slightly away from point B. The incident angle of incident light incident on the point B ′ is θ + δθ, and the refraction angle is θ ′ + δθ ′. △ BB'Q and △ BB'Q_MApplying the triangular sine law to
[0068]
[Expression 12]

[0069]
[Formula 13]

[0070]
The relationship holds. From (Equation 12) and (Equation 13),
[0071]
[Expression 14]

[0072]
It becomes. If both δθ and δθ ′ are very small, (Equation 14) becomes
[0073]
[Expression 15]

[0074]
It becomes. Differentiating both sides of (Equation 9) by θ results in the following.
[0075]
[Expression 16]

[0076]
From (Equation 15) and (Equation 16), when δθ ′ / δθ is eliminated, the meridional paraxial image point Q_MAs an expression representing the position of the following, the following expression is obtained.
[0077]
[Expression 17]

[0078]
From the comparison of (Equation 11) and (Equation 17), when the light ray is obliquely incident on the boundary plane having the refractive index difference, the sagittal paraxial image point Q_SAnd meridional paraxial image point Q_MIt can be seen that does not match.
[0079]
Next, as shown in FIG. 5B, a case is considered in which a parallel plane transparent plate P is disposed obliquely with respect to the optical axis. The thickness of the transparent plate P is t, the refractive index is n, and the refractive index of the external medium of the transparent plate P is n ′.
[0080]
Let Q be the paraxial image point when there is no transparent plate P, B be the incident point when light traveling along the optical axis is incident on the transparent plate P, and C be the exit point. The sagittal paraxial image point corresponding to the point Q by the incident plane of the transparent plate P is Q_S1, Q for the meridional paraxial image point_M1, Point Q by the emission side plane_S1Sagittal paraxial image point corresponding to_S2, Q for the meridional paraxial image point_M2And
[0081]
The following formula is established by (Equation 11) and (Equation 17).
[0082]
[Formula 18]

[0083]
[Equation 19]

[0084]
[Expression 20]

[0085]
[Expression 21]

[0086]
Using the thickness t of the transparent plate P and the incident angle θ of the light beam,
[0087]
[Expression 22]

[0088]
It can be expressed. From FIG. 5B,
[0089]
[Expression 23]

[0090]
[Expression 24]

[0091]
Substituting (Equation 18), (Equation 19), and (Equation 22) into (Equation 23) and (Equation 24), and substituting the results into (Equation 20) and (Equation 21), the following equation is obtained. It is done.
[0092]
[Expression 25]

[0093]
[Equation 26]

[0094]
From (Equation 25) and (Equation 26), the paraxial image point Q corresponding to the paraxial image point Q when the transparent plate P is disposed obliquely with respect to the optical axis._S2, Q_M2Can be requested. If the transparent plate P is not perpendicular to the optical axis, the point Q_S2And point Q_M2Since they do not match, it can be seen that astigmatism occurs.
[0095]
Sagittal paraxial image point Q_S2And meridional paraxial image point Q_M2If the interval of is d,
[0096]
[Expression 27]

[0097]
When (Equation 25) and (Equation 26) are substituted into (Equation 27), and θ ′ is eliminated using (Equation 9), the astigmatic difference d can be obtained by the following equation.
[0098]
[Expression 28]

[0099]
When the medium is air, the refractive index n ′ is 1, and (Equation 28) can be expressed as the following equation.
[0100]
[Expression 29]

[0101]
The configuration shown in FIG. 3 includes a transparent plate 67, dichroic mirrors 68 and 69, second lens groups 64, 65 and 66, and polarization beam splitters 52, 53 and 54 as shown in the model diagram of FIG. Astigmatism is corrected by arranging each of them. Among the arrangement methods, the effects of the second lens groups 64, 65, 66 will be described with reference to the schematic diagram of the projection optical system shown in FIG.
[0102]
Here, when the reflective light valve 91 shown in FIG. 6 corresponds to the reflective light valve 56 shown in FIG. 3, the polarization beam splitter 92, the second lens group 93, and the color combining optics shown in FIG. The plane parallel plates 94, 95, and 96 constituting the system correspond to the polarization beam splitter 53, the transparent plate 67, and the dichroic mirrors 69 and 68 of FIG. Further, the first lens group 97 shown in FIG. 6 corresponds to the first lens group 71 of FIG.
[0103]
The reflected light from the reflection type light valve 91 includes a polarization beam splitter 92, a second lens group 93, dichroic mirrors constituting a color synthesis optical system, transparent planes, parallel plane plates 94, 95, 96 serving as plane mirrors, The light passes through one lens group 97 and is projected on a screen (not shown).
[0104]
A solid line 98 is a light beam when the second lens group 93 is used, and a broken line 99 is a light beam when the second lens group 93 is not provided.
[0105]
Since the projection display apparatus according to the present embodiment uses the reflective light valve 91 and uses the polarizer and the polarizing beam splitter 92 using a multilayer film as the analyzer, the contrast around the projection image is particularly polarized. It depends on the incident angle of the light beam incident on the beam splitter 92. Therefore, the light passing through the polarizing beam splitter 92 is preferably close to telecentric.
[0106]
In order to make the entire apparatus compact as shown in FIG. 3, the optical axes from the reflective light valves 55, 56, 57 to the CRTs 58, 59, 60 are parallel, that is, the polarization beam splitters 52, 53. , 54 are preferably parallel to each other. For this purpose, as shown in FIG. 6, a polarization beam splitter 92 having both a polarization separation function and an astigmatism correction function between the first lens group 97 and the reflective light valve 91, and at least three color synthesis optical systems. A space for arranging parallel plane plates is required. In this case, the back focus of the projection lens is required to be very long. In the present embodiment, an effective display area of the reflective light valve 91 is 2.5 inches diagonal (aspect ratio 3: 4), the focal length of the projection lens is about 78 mm, and the F number is 4.0. The back focus requires at least 320 mm or more, preferably 350 mm or more in terms of air optical path length. If only the first lens group 97 is used to form a projection lens, the light emitted from the polarization beam splitter 92 travels as indicated by a broken line 99 to form a lens on the reflective light valve side of the projection lens and a color synthesis optical system. The parallel flat plates 94, 95, and 96 need to have large diameters. Accordingly, both the projection lens and the color synthesis optical system are very expensive, and the projection lens is heavy.
[0107]
Therefore, if the second lens group 93 having positive power is disposed at a position sufficiently away from the first lens group 97 and the entire projection lens is configured by two groups having a long space, light advances as indicated by a solid line 98. The entire projection optical system can be configured compactly. The second lens group 93 may be used by cutting the periphery into a rectangular shape in accordance with the effective area of the light emitted from the polarization beam splitter 98 using plastic as a material.
[0108]
As described above, the second lens group 93 is disposed between the plane parallel plates 94, 95, and 96 and the polarization beam splitter 92, so that the compactness, telecentricity, and astigmatism correction function of the entire apparatus can be achieved. Can be charged at the same time. This configuration is also effective for an optical apparatus in the case where a parallel plane transparent plate having only a function of correcting astigmatism is arranged instead of the polarizing beam splitter 92.
[0109]
Next, astigmatism generated in the transparent plate 67 and the dichroic mirrors 68 and 69 when the second lens group 64, 65, and 66 having power is arranged will be described with reference to the model diagram shown in FIG. . It is assumed that the light beam travels from the screen side to the reflective light valve side.
[0110]
7 corresponds to the transparent plate 67 and the dichroic mirrors 68 and 69 in FIG. 3, and the lens L corresponds to the second lens groups 64, 65 and 66.
[0111]
The focal length of the lens L is f, and the sagittal paraxial image point without the lens L is Q_aS, Q for the meridional paraxial image point_aM, The astigmatic difference is d₁Sagittal paraxial image point Q from the main plane of lens L_aSIs the sagittal magnification m of the virtual image by the lens L._S, Meridional magnification m_MCan be expressed as:
[0112]
[30]

[0113]
[31]

[0114]
Also, the sagittal paraxial image point when the lens L is arranged is Q_bS, Q for the meridional paraxial image point_bM, The astigmatic difference is d₁′ And sagittal paraxial image point Q from the main plane of lens L_bSThe distance to b_S, Meridional paraxial image point Q_bMThe distance to b_MIf
[0115]
[Expression 32]

[0116]
[Expression 33]

[0117]
[Expression 34]

[0118]
It becomes. From (Equation 30), (Equation 31), (Equation 32), (Equation 33), and (Equation 34), the astigmatic difference d ′ can be expressed by the following equation.
[0119]
[Expression 35]

[0120]
(Equation 35) is d₁If is sufficiently smaller than f and a, it can be approximated as follows.
[0121]
[Expression 36]

[0122]
Therefore, from (Equation 28) and (Equation 36), the astigmatic difference d of the transparent plate P in FIG.₁′ Is the thickness of the transparent plate P t₁, N₁, The refractive index of the medium is n₁′, The incident angle of light on the transparent plate P is θ₁Then, it can obtain | require with following Formula.
[0123]
[Expression 37]

[0124]
On the other hand, the astigmatic difference d generated in the polarization beam splitters 52, 53, and 54 shown in FIG.₂T is the thickness of the polarization separation mirror substrate₂, The refractive index of the substrate is n₂, The refractive index of the liquid n₂′, The light incident angle from the liquid to the polarization separation surface is θ₂Then, the following equation is obtained from (Equation 28).
[0125]
[Formula 38]

[0126]
Astigmatic difference d₂Is a value in the liquid, so that the astigmatic difference d in the air after exiting from the polarization beam splitters 52, 53, 54, that is, in terms of air, is d.₂'D₂'= D₂/ N₂From the relationship of ', the following equation is obtained.
[0127]
[39]

[0128]
Therefore, from (Equation 37) and (Equation 39), the projection optical system shown in FIG. 3 can correct astigmatism by satisfying the following expression.
[0129]
[Formula 40]

[0130]
From (Equation 37) and (Equation 39), the thickness t₁, T₂It can be seen that it is sufficient to satisfy the following equation.
[0131]
[Expression 41]

[0132]
In the configuration shown in FIG. 3, the transparent plate 67 of the color synthesis optical system, the substrates of the dichroic mirrors 68 and 69, and the polarization separation mirror substrate of the polarization beam splitter have the same refractive index. N₁= N₂Furthermore, since the medium of the transparent plate 67 and the dichroic mirrors 68 and 69 is air, n₁Since ′ = 1, (Equation 41) becomes
[0133]
[Expression 42]

[0134]
It becomes.
[0135]
The concept of astigmatism and the correction conditions for astigmatism described above are described with reference to a light beam that passes on or near the optical axis of the projection optical system, and passes through a position away from the optical axis. As the angle between the optical axis and the light beam increases, the exact astigmatism is slightly different from that near the optical axis. However, the basic concept and tendency of astigmatism that occurs when light with imaging performance is transmitted through a parallel flat transparent plate that is inclined with respect to the optical axis is the same. When the thickness is relatively thin, there is no significant difference compared with the vicinity on the optical axis. Therefore, the astigmatism correction condition has a sufficiently large effect for improving the resolution of the entire effective area of the projected image projected by the projection display as shown in FIG.
[0136]
Further, all refractive index values are values at e-line (546.07 nm) that is near the center wavelength of visible light. The refractive index has wavelength dispersion characteristics, and the refractive index slightly differs depending on the wavelength. Strictly speaking, the refractive index may be optimized according to the conditions of the three primary color lights of red, blue, and green. However, the astigmatism correction effect is not particularly problematic even with reference to the e-line, which is the green light that has the highest visibility among visible light and has a dominant influence on the resolution of the projected image.
[0137]
In the present embodiment, the focal length f of the second lens group 64, 65, 66 is 240 mm, and from the main plane of the second lens group to the sagittal paraxial image point when the second lens group 64, 65, 66 is not present. The distance a is 110 mm, and the sagittal magnification m from (Equation 30)_SIs about 0.686. Further, the refractive index n of each of the transparent plate 67, the dichroic mirrors 68 and 69, and the polarization separation mirror substrates of the polarization beam splitters 52, 53 and 54, respectively.₁Is 1.52, the refractive index n of the liquid of the polarizing beam splitters 52, 53, 54₂Is 1.44, the light incident angle θ from the medium (air) side to the transparent plate 67 and the dichroic mirrors 68 and 69.₁Is 45 °, and the incident angle θ of the light incident on the polarization separation mirror 84 of the polarization beam splitter 52, 53, 54 from the liquid side.₂Is 55.6 °. From (Equation 42), t₂/ T₁Becomes 0.668.
[0138]
Here, the surface accuracy of the light reflecting surfaces of the dichroic mirrors 68 and 69 and the flat mirror 70 shown in FIG. 3 greatly affects the resolution performance of the projection optical system, and this surface accuracy greatly depends on the thickness condition of the substrate. It depends. When displaying a high-resolution projected image such as a high-definition image, the surface accuracy of each reflecting surface is deformed to be either concave or convex with respect to an ideal flat surface (the radius of curvature is infinite). The curvature radius is required to be at least ± 2λ (λ is the center wavelength of incident light) or less, preferably ± λ or less.
[0139]
If the thickness of the substrate is thin, the surface accuracy is likely to be deteriorated due to the stress when the dielectric multilayer film is deposited or the pressure of peripheral mechanism components when it is incorporated and fixed in the apparatus. The effective areas of the dichroic mirrors 68 and 69 and the plane mirror 70 of the present embodiment each require at least 80 mm × 60 mm or more, and at least 1.5 mm or more in order to satisfy the above surface accuracy conditions even after surface polishing. Preferably, a substrate thickness of 2 mm or more is required. Of these, the plane mirror 70 is a surface mirror, and there is no problem because a sufficiently thick substrate can be used. However, if the substrate is too thick, the dichroic mirrors 68 and 69 pass through positions away from the optical axis of the projection optical system. It becomes difficult to correct the astigmatism of the light beam. Therefore, the substrate thickness is desirably at least 3.0 mm or less, preferably 2.5 mm or less.
[0140]
From the above, the substrate thickness of the dichroic mirrors 68 and 69 is preferably 1.5 mm or more and 3.0 mm or less. Further, since the polarization beam splitters 52, 53, and 54 only transmit light from the reflection type light valves 55, 56, and 57 in the optical path of the projection optical system, the influence of resolution deterioration due to the surface accuracy of the polarization separation mirror substrate is not affected. You may think that there is almost no.
[0141]
Accordingly, in the present embodiment, the thickness t of the transparent plate 67 and the dichroic mirrors 68 and 69 is determined.₁Is about 2.0 mm, and the thickness t of the polarization separation mirror substrate is calculated from the calculation result of (Expression 42)₂Is about 1.3 mm. By doing so, astigmatism as a whole of the projection optical system can be corrected well, and a high-resolution projection image can be displayed.
[0142]
In the above description, the astigmatism generated in the transparent plate 67 and the dichroic mirrors 68 and 69 of the color synthesis optical system is reduced by the square of the virtual image magnification m of the second lens group (64, 65, 66). In addition, a case has been described in which the reduced astigmatism is configured to cancel out by the astigmatism generated in the polarization separation mirror 84 of the polarization beam spiriter (52, 53, 54).
[0143]
In the following, unlike the above embodiment, the second lens unit is not provided, and the astigmatism generated in the color synthesis optical system is canceled by the astigmatism generated in the polarization separation mirror 84. This is a specific example.
[0144]
That is, in this case, in the above (Equation 42), m_sThis corresponds to the case of = 1. Therefore, the virtual image magnification of the second lens group is m_sIn the above embodiment where = 0.686, t₂/ T₁= 0.668 was derived, where (Equation 42) is t₂/ T₁= 0.668 / 0.686²= 1.419.
[0145]
From this, t₁= 2.0 mm, t₂= 2.839 mm, and in this case, the thickness of the polarization separation substrate of the polarization beam splitter may be 2.84 mm.
[0146]
The configuration of the illumination optical system in the configuration shown in FIG. 3 will be described below with reference to FIG. Although not shown in the configuration diagram of FIG. 3, if the relay lenses 105 and 106 are arranged in the optical path until the radiated light from the light source 41 illuminates the reflection type light valves 55, 56 and 57, as shown in FIG. Good. The reflective light valve 107 is the same as the reflective light valves 55, 56, and 57 shown in FIG. Between the first relay lens 105 and the second relay lens 106, a color separation optical system composed of the dichroic mirrors 43, 44, 45 shown in FIG. 3, front polarizers 46, 47, 48, a plane Mirrors 49, 50, 51 are disposed, and polarization beam splitters 52, 53, 54 are disposed between the second relay lens 106 and the reflective light valve 108. The light source 41 includes a lamp 101 and an ellipsoidal mirror 102. The lamp 101 is a xenon lamp, and emits light including three primary color components. The ellipsoidal mirror 102 is made of glass, and an aluminum thin film layer is coated on the reflecting surface. Note that a multilayer film that transmits infrared light and reflects visible light may be deposited on the light reflecting surface.
[0147]
The emitted light of the lamp 101 is reflected by the elliptical mirror 102, the infrared light is removed by the cold mirror 103, and the light is condensed on the second focal point 104 of the elliptical mirror 102. After passing through the second focal point 104, the diverged light is converted into light that is nearly parallel by the first relay lens 104. Since the dichroic mirror using the dielectric multilayer film has a characteristic that the spectral performance changes depending on the incident angle dependency of the light beam, it is desirable that the light passing through the dichroic mirror is as parallel as possible. Nearly parallel light is condensed again by the second relay lens 106 and illuminates the reflective light valve 107. The relay lenses 105 and 106 have a role of efficiently illuminating the image of the lamp 101 formed on the second focal point 103 of the ellipsoidal mirror 102 with an enlargement magnification corresponding to the effective display area of the reflective light valve 107.
[0148]
In FIG. 8, the first relay lens 105 is composed of two lenses, but it may be one, or three or more. Further, the second relay lens 106 is a plane mirror that leads to the color separation optical system shown in FIG. 3 and the front polarizers 46, 47, 48, or to the front polarizers 46, 47, 48 and the polarization beam splitter. You may arrange | position between 49,50,51. Furthermore, in this embodiment, a xenon lamp is used as the lamp 101, but a metal halide lamp, a halogen lamp, or the like may be used instead.
[0149]
Hereinafter, a detailed configuration of the front polarizers 46, 47, and 48 will be described with reference to FIG.
[0150]
A V-shaped groove is formed inside the frame body 111, and the end portions of the polarization-selective mirrors 114 and 115 are inserted into the groove so that the respective cross sections are V-shaped. The space of the container constituted by the frame 111, the entrance window 112 made of a glass substrate, the exit window 113, and the polarization separation mirrors 114 and 115 is filled with a liquid 116. The liquid material and the multilayer structure of the polarization separation mirrors 114 and 115 are the same as those of the polarization beam splitters 52, 53, and 54 shown in FIG.
[0151]
As shown in FIG. 9, the natural light 117 incident perpendicularly to the front polarizers 46, 47 and 48 passes through the incident window 112 and the liquid 116 and enters the polarization separation mirror 114 at an angle of 55.6 °. The natural light 117 is separated into the S-polarized light component 118 and the P-polarized light component 119 by the polarization separation mirror 114, respectively. The P-polarized light component 119 passes through the liquid 116 and is emitted from the exit window 113, and the S-polarized light component 118b is a frame. Each incident on the inner wall of 111.
[0152]
In order to ensure the compactness of the front polarizers 46, 47, 48, the number of polarization separation mirrors 114, 115 is two, and they are arranged symmetrically in a V shape with respect to the optical axis. The V-shaped apex may be arranged toward the light source so that unnecessary S-polarized light components reflected by the polarization separation mirrors 114 and 115 do not travel toward the exit window 113. When the number of polarization separation mirrors is one, not only the dimension in the optical axis direction becomes large, but also the incident angle dependency becomes asymmetric when light is incident obliquely on the front polarizer, and this influence is projected image The problem that it is easy to appear. Also, it may be arranged in a zigzag shape using three or more polarization separation mirrors, but in the case of an odd number, the arrangement of the polarization separation mirrors is asymmetric with respect to the optical axis, so the configuration of an even number is better. preferable. Furthermore, after the S-polarized light component that becomes unnecessary light is reflected by the polarization separation mirror, it may enter the adjacent polarization beam splitter, and a part of the multiple reflected light may travel to the exit window side. Note that if this unnecessary polarization component reaches the polarization beam splitters 52, 53, 54 and the reflection type light valves 55, 56, 57 shown in FIG. 3, the contrast performance of the projected image may be significantly deteriorated. Cost. Thus, it can be seen that the pre-polarizer having the configuration shown in FIG. 9 can efficiently extract light close to linearly polarized light.
[0153]
The prepolarizer and the polarizing beam splitter are arranged so that the P-polarized light emitted from the prepolarizer is reflected as S-polarized light by the polarizing beam splitter. In general, the incident light is spread over a certain angle range around the optical axis, and the wavelength of the incident light is not a single wavelength. By increasing the number of layers of the dielectric multilayer film, it is relatively easy to approach 100%, but it is difficult to make the transmittance of P-polarized light approach 100%. Therefore, it is preferable to extract P-polarized light with a front polarizer that needs to cut unnecessary polarization components. Because the linearly polarized light incident on the polarizing beam splitter is efficiently guided to the reflective light valve side, and in the case of black display, the readout light reflected from the reflective light valve must be cut by the polarizing beam splitter. It is preferable that the polarization component incident on the polarization beam splitter is S-polarized light. By doing so, a high-contrast projected image can be displayed.
[0154]
The projection display apparatus of the present invention shown in FIG. 3 uses the second lens groups 64, 65, 66, so that the projection optical system is compact, but the light passing through the polarization beam splitters 52, 53, 54 is compact. It has the performance of good telecentricity. Therefore, the principal ray incident on the polarization separation surface of the polarization beam splitter is substantially parallel to the optical axis of the projection optical system, and the polarization separation performance is hardly deteriorated due to the dependency of the light incident angle on the polarization separation surface. Therefore, it is possible to display a high-quality projected image that does not have a problem of contrast reduction or non-uniformity of the projected image caused by deterioration of polarization separation performance.
[0155]
Further, since the configuration shown in FIG. 3 has substantially one projection lens, color shading does not occur. Further, the illumination light path lengths from the light source 41 to the respective reflection type light valves 55, 56, 57 are equal in three colors, and the screen centers of the respective reflection type light valves 55, 56, 57 are located on the optical axis of the projection lens. Therefore, the occurrence of uneven color is small.
[0156]
In this embodiment, three CRTs, a writing lens, a reflective light valve, a polarizing beam splitter, and a second lens group are arranged in the horizontal direction of the CRT screen, but they are arranged in the vertical direction of the CRT screen. Also good.
[0157]
In this embodiment, a CRT is used as an image source. However, for example, a transmissive TFT liquid crystal panel is used and illuminated from the rear by a light source such as a metal halide lamp, and is formed on the liquid crystal panel according to a video signal. The optical image may be formed on the photoconductive layer of the reflective light valve by a writing lens. The writing optical system may also use an optical fiber bar used as an image guide in addition to the writing lens.
[0158]
Other embodiments of the present invention will be described below.
[0159]
FIG. 10 is a configuration diagram of the projection optical system when only the configuration of the color synthesis optical system is different in the projection display device shown in FIG.
[0160]
The color synthesizing optical system includes plane mirrors 130 and 133 and dichroic mirrors 131 and 132.
[0161]
The light from the reflective light valve 121 passes through the polarization beam splitter 124 and the second lens group 127, then passes through the two dichroic mirrors 131 and 132, and enters the first lens group 134. The light from the reflection type light valve 122 is transmitted through the polarization beam splitter 125 and the second lens group 128, and then reflected by the plane mirror 130 and the dichroic mirror 131 in which a parallel plane transparent plate is joined to the surface mirror, and the dichroic mirror. The light passes through 132 and enters the first lens group 134. Further, the light from the reflection type light valve 123 is transmitted through the polarization beam splitter 126 and the second lens group 129, then reflected by the back mirror of the surface mirror 133 and the dichroic mirror 132 and incident on the first lens group 134. .
[0162]
The reflecting surfaces of the plane mirrors 130 and 133 and the color combining surfaces of the dichroic mirrors 131 and 132 are both inclined by 45 ° with respect to the optical axis of the projection optical system. Also, the substrates of the dichroic mirrors 131 and 132 and the transparent plate joined to the reflecting surface of the plane mirror 130 are the same as those of the various substrates shown in FIG.
[0163]
The color synthesizing optical system of the projection optical system shown in FIG. 10 has light reflected from the three reflective light valves 121, 122, and 123 by substantially reflecting the reflecting surfaces of the plane mirror 130 and the dichroic mirror 132, respectively. The astigmatism correction conditions are the same.
[0164]
In consideration of the conditional expression (Equation 40) and the surface accuracy of the reflection surfaces of the dichroic mirrors 131 and 132, the substrate thickness t of the polarization separation mirrors of the polarization beam splitters 124, 125, and 126 is considered.₂Is 2 mm, the substrate thickness of the transparent plate joined to the reflecting surface of the plane mirror 130 is 0.75 mm, and the substrate thicknesses of the dichroic mirrors 131 and 132 are 1.5 mm, respectively. Total thickness t₁Are set to 3.0 mm.
[0165]
In this case, the substrate thickness t of (Equation 41)₁, T₂Is a value represented by the following equation.
[0166]
[Equation 43]

[0167]
(44)

[0168]
Here, i is the number of sheets that pass through the parallel plane plate of the color synthesis optical system, and j is the number of parallel planes provided to correct astigmatism generated in the color synthesis optical system. In the case of back surface reflection, it is considered that two parallel flat plates are transmitted per reflection.
[0169]
In the embodiment shown in FIG. 10, j is 1 for each of the optical paths from the reflective light valves 121, 122, and 123, but for i, the optical path from the reflective light valve 121 is 2, and the reflective The light path from the mold light valve 122 is 3, and the light path from the reflection light valve 123 is 2.
[0170]
As described above, in the embodiment shown in FIG. 10, the color synthesizing optical system is configured when light rays pass through a plurality of plane-parallel plates and when back-reflection is used under the same conditions as when passing twice. However, the concept of astigmatism correction and the basic formula of the correction condition (Equation 40) can be applied as they are.
[0171]
In the above embodiment, the reflection type light valve that modulates the polarization state of the readout light with the liquid crystal layer according to the image written in the photoconductive layer is used as the light valve. However, other types of liquid crystal panels and electro-optic crystals are used. Any reflective type that forms an optical image as a change in birefringence can be used as a light valve.
[0172]
In addition, the concept and method for correcting astigmatism of the present invention is based on optical characteristics such as a transmissive light valve or a light modulation method such as a scattering, diffraction, or light deflection type light valve. Anything that forms an image can be applied.
[0173]
  Less thanAs a reference example of the present invention,An embodiment of a projection apparatus configured using a transmissive light valve will be described with reference to FIG.
[0174]
The transmission type light valves 150, 151, and 152 are TFT liquid crystal cells using twisted nematic liquid crystal as a light modulation material, and polarizers used as polarizers and analyzers before and after the TFT liquid crystal cell.
[0175]
Light emitted from the light source 141 absorbs or reflects ultraviolet light and infrared light, passes through a UV-IR cut filter 142 that transmits only visible light, and a plane mirror 143, and then reaches dichroic mirrors 144 and 145 and a plane mirror 146. Are separated into three primary color lights of red, green and blue. The three primary color lights are sequentially incident on the corresponding field lenses 147, 148, and 149 and the transmissive light valves 150, 151, and 152, respectively.
[0176]
The color synthesizing optical system includes a plane mirror 153 and dichroic mirrors 154 and 155. The projection lens includes second lens groups 156 and 157 having a positive power and a first lens group 158. In addition, the reflecting surface of the flat mirror 153 and the color combining surfaces of the dichroic mirrors 154 and 155 are both inclined by 45 ° with respect to the optical axis of the projection lens.
[0177]
Light emitted from the light valves 150, 151, and 152 is combined into one by a color combining optical system, and enlarged and projected on a screen by a projection lens.
[0178]
As described above, the light reflecting surfaces of the plane mirror 153 and the dichroic mirrors 154 and 155 constituting the color synthesis optical system are required to have high surface accuracy, and the surface accuracy greatly depends on the substrate thickness. In particular, this surface accuracy has a greater influence on the resolution of the projected image as the position of the reflecting surface is closer to the principal point of the projection lens. That is, the condition of the surface accuracy of the light reflecting surface of the dichroic mirror 155 becomes stricter than that of the plane mirror 153 and the dichroic mirror 154.
[0179]
Therefore, in the configuration shown in FIG. 11, the second lens groups 156 and 157 that are separated from the first lens group 158 are arranged between the plane mirror 153, the dichroic mirror 154, and the dichroic mirror 155, respectively. By doing so, as can be seen from (Equation 36), the astigmatic difference generated in the dichroic mirror 155 viewed on the light valve 150, 151, 152 side is positive power compared to the case without the second lens group 156. Can be reduced by the square of the virtual image magnification by the second lens group having. Therefore, the substrate thickness of the dichroic mirror 155 can be made thicker than when the second lens group 156 is not provided, and the reflecting surface of the dichroic mirror 155 can have high surface accuracy without increasing astigmatism. .
[0180]
The embodiment shown in FIG. 11 does not completely correct the astigmatism generated in the color synthesizing optical system on the paraxial axis of the projection optical system. However, the concept of astigmatism of the optical apparatus of the present invention is as follows. This is the same, and the effect of using the second lens group 156 is great.
[0181]
In the optical path passing through the second lens group 157, the light emitted from the light valve 152 is only reflected by the plane mirror 153 and the dichroic mirror 155, and therefore there is no cause for astigmatism. Therefore, the second lens group 157 does not exhibit the effect of reducing astigmatism. However, since the first lens group 158 and the second lens groups 156 and 157 are integrated lens systems having imaging performance, the second lens group 157 is necessary for imaging performance.
[0182]
Also in the configuration of FIG. 11, the plane including the normal of the parallel plane and the optical axis of the projection lens, and the dichroic mirrors 154 and 155 between the light valves 150, 151, and 152 and the first lens group 158. Astigmatism may be corrected by providing a space in which a transparent plate is disposed so that planes including the normal of the color synthesis surface and the optical axis of the projection lens are orthogonal to each other.
[0183]
  more than,As shown in FIG.Reference exampleIn this case, the transmission type light valve is used. However, if a projection optical system having a color synthesis optical system is used, the same effect can be obtained even when a reflection type light valve is used.
[0184]
As described above, according to the present invention, it is possible to satisfactorily correct astigmatism generated in the color synthesis optical system, and to make the projection optical system compact. Therefore, by using the optical device of the present invention for a projection display device, a projection image with a very high resolution can be displayed even in the case of a projection optical system having a color synthesis optical system and composed of one projection lens. effective.
[0185]
In the above embodiment, in order to obtain a full-color projection image, a projection display device that uses three light valves for red, green, and blue, or an optical correction method that is used in such a device. Although described above, the present invention is not limited to this. For example, an optical apparatus that forms and outputs an optical image of monochromatic light, or an optical correction method used in such an optical apparatus may be used.
[0186]
  Moreover, in the said embodiment, the 2nd lens group as the 2nd lens means of this invention, and the polarization separation mirror as a transparent substrate of the polarization separation means of this invention, As a plane board member of this invention, Reduce the astigmatism generated by the dichroic mirror of the color synthesis optical system (or increase the surface accuracy of the dichroic mirror without increasing the astigmatism), and cancel the astigmatism. The projection display apparatus in the case of correcting to the above or the optical correction method used for such an apparatus has been described.On the other hand, as a reference example of the present invention,For example, an optical correction method used for an apparatus having a second lens unit without the transparent substrate of the polarization separating unit or an apparatus having such a configuration may be used. In this case, as can be seen from the above (Equation 36), for example, the astigmatism generated in the transparent plate 67 and the dichroic mirrors 68 and 69 of the color synthesis optical system shown in FIG. 65, 66), the effect of being able to be reduced by the square of the virtual image magnification m. Alternatively, as another effect, the substrate thickness of the dichroic mirror can be further increased without increasing the astigmatism as compared with the case where the second lens group is not provided. There is also an effect that the reflective surface can be made with high surface accuracy.
[0187]
  In the above embodiment, the case where the polarization separation means of the present invention has a transparent substrate having a predetermined thickness on which a film having polarization selection characteristics is formed has been described.. On the other hand, as a reference example of the present invention,For example, the polarization separation means may have a configuration in which a thin film having polarization selection characteristics is provided and both sides of the thin film are held by prism-shaped members. Even in this case, for example, astigmatism generated in the transparent plate 67 and the dichroic mirrors 68 and 69 of the color synthesis optical system shown in FIG. 3 is reduced to 2 of the virtual image magnification m of the second lens group (64, 65, 66). Demonstrates the effect of being able to make it smaller by the factor.
[0188]
The advantages of the optical apparatus according to the optical correction method of the present invention are that the astigmatism generated in the color synthesis optical system can be corrected satisfactorily and the projection optical system can be made compact. Therefore, the projection display device using the optical device of the present invention can display a projected image with a very high resolution even when it is composed of one projection lens having a color synthesis optical system.
[0189]
【The invention's effect】
As is apparent from the above description, the present invention has the advantage that astigmatism can be corrected more satisfactorily than in the prior art. In addition, the present invention has an advantage that it can display a projected image with a higher resolution than in the past.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining astigmatism in an embodiment of the present invention.
FIG. 2A is a schematic configuration diagram illustrating an astigmatism correction method in which two parallel flat transparent plates P1 and P2 whose incident surfaces are orthogonal to each other are arranged in the present embodiment.
(B): Astigmatism generated in the first lens unit L1, the parallel flat transparent plate P1 serving as the dichroic mirror of the color synthesis optical system, the second lens unit L2, and the transparent plate P1 in the present embodiment. Schematic configuration diagram explaining an astigmatism correction method by a configuration in which a parallel plane transparent plate P2 and a light valve LV are arranged to correct
FIG. 3 is a perspective view showing a configuration of an embodiment of a projection display apparatus of the present invention.
FIG. 4 is a cross-sectional view showing the configuration of the polarizing beam splitter of the present embodiment
FIG. 5A is an explanatory diagram for explaining the principle of astigmatism when convergent light is obliquely incident on a boundary plane A having a refractive index difference in the present embodiment.
(B): Explanatory drawing explaining the principle of astigmatism when the transparent plate P of a parallel plane in this embodiment is disposed obliquely with respect to the optical axis.
FIG. 6 is a schematic configuration diagram of a projection optical system according to an embodiment of the optical apparatus of the present invention.
FIG. 7 is an explanatory diagram for explaining an astigmatic difference amount in the present embodiment.
FIG. 8 is a schematic configuration diagram of an illumination optical system according to an embodiment of the optical apparatus of the present invention.
FIG. 9 is a cross-sectional view showing a configuration of a front polarizer according to an embodiment of the optical device of the present invention.
FIG. 10 is a schematic configuration diagram of a projection optical system of an optical device according to another embodiment of the present invention.
FIG. 11 shows the present invention.Reference exampleSchematic configuration diagram of optical device
FIG. 12 is a schematic cross-sectional view showing the basic configuration of a reflective light valve
FIG. 13 is a perspective view illustrating a configuration example of a conventional optical device.
[Explanation of symbols]
41 Light source
43, 44, 45, 68, 69 Dichroic mirror
46, 47, 48 Pre-deflector
49, 50, 51, 70 Flat mirror
52, 53, 54, 92 Polarizing beam splitter
55, 56, 57, 91 Reflection type light valve
58, 59, 60 CRT
61, 62, 63 Writing lens
L2, 64, 65, 66, 93 Second lens group
P, P1, P2, 67, 94, 95, 96 Transparent plate
L1, 71, 97 First lens group

Claims (9)

An image forming means for forming an optical image;
First lens means disposed forward on the optical axis of the image forming means;
A second lens unit disposed between the image forming unit and the first lens unit and having a positive power;
A first plane plate member disposed between the first lens means and the second lens means, constituting a color composition means, and transmitting the optical image ;
Wherein the second lens means disposed between the image forming means, have a polarization separation performance, and a second flat plate member that transmits the optical image,
The first lens means and the second lens means are combined so as to enlarge and project the optical image on the image forming means on a screen,
The second flat plate member is a transparent substrate having a predetermined thickness provided with a thin film having polarization selection characteristics on one side and having polarization separation performance,
The first and second planar plate members are disposed obliquely with respect to the optical axis formed by the first and second lens means,
A plane including a normal to the plane of the first plane plate member and an optical axis of the first and second lens means; a normal to the plane of the second plane plate member; and the first and second The plane including the optical axis of the lens means is orthogonal to each other,
It said first plane plate member thickness t ₁ and the relationship between the thickness t ₂ of the second flat plate member, an optical device which satisfies the following equation.

Where m _S is the virtual image magnification at the sagittal paraxial image point of the second lens means, n ₁ is the refractive index of the first plane plate member, and n ₁ ′ is the medium of the first plane plate member Refractive index, θ ₁ is the incident angle of the light beam on the optical axis of the first and second lens means entering the flat plate member from the medium of the first flat plate member, and n ₂ is the second flat plate. The refractive index of the face plate member, n ₂ ′ is the refractive index of the medium of the second flat plate member, and θ ₂ is incident on the second flat plate member from the medium of the second flat plate member. And the incident angle of the light on the optical axis of the second lens means.   The optical apparatus according to claim 1, wherein a thickness of the first flat plate member is 1.5 mm or greater and 3.0 mm or less. If the first and second flat plate member is provided with a plurality each of the plate thickness t ₁ and the thickness t ₂ is according to claim 1, characterized by being represented by the following formula Optical device.

Here, t _1i (i = 1, 2, 3...) Is a plate thickness of the i-th flat plate member of the plurality of first flat plate members, and t _2j (j = 1, 2, 3... Are the plate thicknesses of the j-th flat plate member of the plurality of second flat plate members. It said image forming means, the optical device according to claim 1, characterized in that a reflective light valve that modulates a polarization direction of light. An image forming unit that forms an optical image, a first lens unit that is disposed forward on the optical axis of the image forming unit, and a positive power disposed between the image forming unit and the first lens unit. A first plane plate member disposed between the first lens unit and the second lens unit, constituting a color synthesis unit and transmitting the optical image ; disposed between the image forming means and said second lens means, have a polarization separation performance, and a second flat plate member that transmits the optical image, the said first lens means the Two lens means are combined to enlarge and project the optical image on the image forming means on a screen, and the second flat plate member is provided with a thin film having polarization selection characteristics on one side, A transparent substrate having a predetermined thickness and having polarization separation performance It said first and second plane plate member is an optical compensation method of an optical device which is arranged obliquely to make the optical axis of said first and said second lens means,
A plane including a normal to the plane of the first plane plate member and an optical axis of the first and second lens means; a normal to the plane of the second plane plate member; and the first and second The planes including the optical axis of the lens means are orthogonal to each other, and astigmatism caused by the first plane plate member and the second plane plate member is corrected with respect to each other. optical correction method characterized by faceplate the relationship between the thickness t ₁ and the thickness t ₂ of the second flat plate member of the member is adjusted so as to satisfy the following equation.

Where m _S is the virtual image magnification at the sagittal paraxial image point of the second lens means, n ₁ is the refractive index of the first plane plate member, and n ₁ ′ is the medium of the first plane plate member Refractive index, θ ₁ is the incident angle of the light beam on the optical axis of the first and second lens means entering the flat plate member from the medium of the first flat plate member, and n ₂ is the second flat plate. The refractive index of the face plate member, n ₂ ′ is the refractive index of the medium of the second flat plate member, and θ ₂ is incident on the second flat plate member from the medium of the second flat plate member. And the incident angle of the light on the optical axis of the second lens means. If the first and second flat plate member is provided with a plurality each of the plate thickness t ₁ and the thickness t ₂ is according to claim 5, characterized by being represented by the following formula Optical correction method.

Here, t _1i (i = 1, 2, 3...) Is a plate thickness of the i-th flat plate member of the plurality of first flat plate members, and t _2j (j = 1, 2, 3... Are the plate thicknesses of the j-th flat plate member of the plurality of second flat plate members. A light source that emits light containing color components of the three primary colors;
Color separation means for separating the emitted light of the light source into three primary color lights;
Three pre-polarizers on which each of the three output lights of the color separation means is individually incident;
A plurality of image forming means for forming an optical image as a change in birefringence;
A polarization separation unit that is provided for each of the image forming units and separates polarization components whose polarization planes are orthogonal to each other;
They provided for each polarization separator, transmits the light from the polarization separating means, a second lens having a Seipa word,
Color synthesizing means for synthesizing light from each of the polarization separating means into one;
A first lens that emits the light emitted from the color synthesizing unit.
Each of the polarization separating means has a transparent substrate that is parallel to the optical axis of the first lens and transmits the optical image, and a dielectric having polarization selectivity on the transparent substrate. Body multilayer film is formed,
The color synthesizing means , for two of the three primary color lights, is a dielectric multi-layer having wavelength selectivity on a transparent plane parallel plane arranged obliquely with respect to the optical axis of the first lens. film was formed, the two light has been configured to include a dialog black dichroic mirror which transmits respectively, for the remaining one light among the three primary color light, the optical axis of said first lens An anti-reflection treatment is performed on both surfaces of a parallel flat transparent substrate disposed obliquely, and includes an optical correction plate that transmits the remaining one light,
Each of the first lenses and each of the second lenses are combined so as to enlarge and project the optical image on the image forming unit onto a screen,
The color for the remaining one of the three primary color lights or the normal of the dielectric multilayer film forming surface of each dichroic mirror of the color synthesizing unit for the two lights of the three primary color lights. A plane including a normal line of the antireflection surface of the optical correction plate of the combining means and the optical axes of the first lens and the second lens; a normal line of the dielectric multilayer film forming surface of each polarization separating means; The planes including the optical axes of the first lens and the second lens are orthogonal to each other,
The thickness of the dichroic mirror of the color synthesizing unit for the two lights among the three primary color lights, and the optical of the color synthesizing unit for the remaining one of the three primary color lights A projection type characterized in that a plate thickness t ₁ which is a plate thickness of the correction plate and a plate thickness t _{2 of the} transparent substrate of the polarization separation means corresponding to the three primary color lights satisfy the following conditions: Display device.

Where m _S is the virtual image magnification at the sagittal paraxial image point of the second lens, n ₁ is the refractive index of the dichroic mirror substrate or the optical correction plate , and n ₁ ′ is the medium of the dichroic mirror or the optical correction plate . , Θ ₁ is the incident angle of the light beam on the optical axis of the first lens or the second lens, and n ₂ is the transparent substrate of the polarization separating means, which is incident on the dichroic mirror or the optical correction plate from the medium. refractive index, n2 'is a medium refractive index of the polarization separator, the theta ₂ enters the polarization splitting surface of the polarization separation means from said medium, of said first lens or the second lens of the optical axis on the ray Incident angle.   The polarization separating means is a prism as a whole by bringing a liquid or solid having a refractive index different from the refractive index of the transparent substrate on which the dielectric multilayer film having polarization selectivity is formed, and both surfaces of the transparent substrate into close contact with each other. 8. The projection display device according to claim 7, wherein the projection display device has a shape. 8. The projection display device according to claim 7, wherein thicknesses of the dichroic mirror and the optical correction plate are 1.5 mm or more and 3.0 mm or less.

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